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Authors: Xue Huang, Li Zheng and Rangjin Xie.
The Journal of Horticultural Science and Biotechnology (2021)
Abstract: "In citrus, post-harvest treatment with ethylene or ethephon in an airtight container frequently resulted in fruit calyx drying, browning and abscission, with a consequent reduction in commercial value. To avoid these problems, pre-harvest degreening with ethepnon was performed on ‘CARA CARA’ navel orange fruits. An earlier and deeper orange colour development was obtained after treatment, reflecting at higher lightness (L*) and a*/b* ratio. The total carotenoid content in flavedo significantly increased, paralleling with a remarkable decrease in chlorophyll content, while in flesh TSS, TA and Vc were all not affected. A transcriptome analysis revealed that 171 genes in flavedo were involved in ethylene-degreening. These ethylene-responsive genes were involved in photosynthesis, chloroplast biogenesis, sugar metabolism, secondary metabolism, and activation of regulatory processes, including transcription regulation and protein posttranslational modification. In the chlorophyll metabolism, a chlorophyllase gene was strikingly increased, indicating the role of ethylene in promoting chlorophyll degradation. While, the genes related to carotenoid metabolism did not show any significant expression change after ethephon treatments. In conclusion, our data showed that pre-harvest degreening was an effective method to accelerate colour improvement, and meanwhile created a solid foundation for future investigations on the molecular mechanism underlying degreening of orange fruits."
Authors: Kapil Sharma, Soni Gupta, Supriya Sarma, Meenakshi Rai, Yellamaraju Sreelakshmi and Rameshwar Sharma.
The Plant Journal (2021)
Abstract: "The role of ethylene in plant development is mostly inferred from its exogenous application. The usage of the mutants affecting ethylene biosynthesis proffers a better alternative to decipher its role. In tomato, 1‐aminocyclopropane carboxylic acid synthase2 (ACS2) is a key enzyme regulating ripening‐specific ethylene biosynthesis. We characterized two contrasting acs2 mutants; acs2‐1 overproduces ethylene, has higher ACS activity, and increased protein levels, while acs2‐2 is an ethylene under‐producer, displays lower ACS activity and protein levels than wild type. Consistent with high/low ethylene emission, the mutants show opposite phenotypes, physiological responses, and metabolomic profiles than the wild type. The acs2‐1 showed early seed germination, faster leaf senescence, and accelerated fruit ripening. Conversely, acs2‐2 had delayed seed germination, slower leaf senescence, and prolonged fruit ripening. The phytohormone profiles of mutants were mostly opposite in the leaves and fruits. The faster/slower senescence of acs2‐1/acs2‐2 leaves correlated with the endogenous ethylene/zeatin ratio. The genetic analysis showed that the metabolite profiles of respective mutants co‐segregated with the homozygous mutant progeny. Our results uncover that besides ripening, ACS2 participates in the vegetative and reproductive development of tomato. The distinct influence of ethylene on phytohormone profiles indicates the intertwining of ethylene action with other phytohormones in regulating plant development."
Authors: Sylwia Struk, Carolien De Cuyper, Anse Jacobs, Lukas Braem, Alan Walton, Annick De Keyser, Stephen Depuydt, Lam Dai Vu, Ive De Smet, François-Didier Boyer, Dominique Eeckhout, Geert Persiau, Kris Gevaert, Geert De Jaeger and Sofie Goormachtig.
Molecular & Cellular Proteomics (2021)
Abstract: "The F-box protein MORE AXILLARY GROWTH 2 (MAX2) is a central component in the signaling cascade of strigolactones (SLs) as well as of the smoke derived karrikins (KARs) and the so far unknown endogenous KAI2 ligand (KL). The two groups of molecules are involved in overlapping and unique developmental processes, and signal-specific outcomes are attributed to perception by the paralogous α/β-hydrolases DWARF14 (D14) for SL and KARRIKIN INSENSITIVE 2/ HYPOSENSITIVE TO LIGHT (KAI2/HTL) for KAR/KL. Additionally, depending on which receptor is activated, specific members of the SUPPRESSOR OF MAX2 1 (SMAX1) – LIKE (SMXL) family control KAR/KL and SL responses. As proteins that function in the same signal transduction pathway often occur in large protein complexes, we aimed at discovering new players of the MAX2, D14 and KAI2 protein network by tandem affinity purification using Arabidopsis cell cultures. When using MAX2 as a bait, various proteins were co-purified among which general components of the Skp1-Cullin-F-box complex and members of the CONSTITUTIVE PHOTOMORPHOGENIC 9 signalosome. Here, we report the identification of a novel interactor of MAX2, a type 5 serine/threonine protein phosphatase, designated PHYTOCHROME-ASSOCIATED PROTEIN PHOSPHATASE 5 (PAPP5). Quantitative affinity purification pointed at PAPP5 as being more present in KAI2 rather than D14 protein complexes. In agreement, mutant analysis suggests that PAPP5 modulates KAR/KL-dependent seed germination in suboptimal conditions and seedling development. Additionally, a phosphopeptide enrichment experiment revealed that PAPP5 might dephosphorylate MAX2 in vivo independently of the synthetic strigolactone analog, rac-GR24. Together, by analyzing the protein complexes to which MAX2, D14 and KAI2 belong, we revealed a new MAX2 interactor, PAPP5, that might act through dephosphorylation of MAX2 to control mainly KAR/KL- related phenotypes and, hence, provide another link with the light pathway."
Authors: Qingqing Cui, Lulu Xie, Chunjuan Dong, Lihong Gao and Qingmao Shang.
Plant Science (2021)
Highlights: • Gene co-expression networks during graft formation are stage-specific. • The asymmetric response phase (3−72 hours after grafting) is the critical period for graft formation. • Auxin and cytokinin respond to grafting, above and below the graft junction, respectively, to promote the graft formation. • The accumulation of auxin above the graft junction prepares cells for mitosis, which promotes cell division to form callus. • Exogenous application of certain concentrations of IAA and 6-BA will promote graft formation.
Abstract: "Grafting is widely used worldwide because of its obvious advantages, especially in solanaceous vegetable crops. However, the molecular mechanisms underlying graft formation are unknown. In this study, internode tissues from above and below the graft junction were harvested, and we performed weighted gene co-expression network analysis (WGCNA) to describe the temporal and spatial transcriptional dynamics that occur during graft formation in tomato. The wounding stress response involved in JA, ETH, and oxylipins mainly occurred at 1 h after grafting (HAG). From 3 to 12 HAG, the biological processes of snRNA and snoRNA modification and the gibberellin-mediated signaling pathway functioned both above and below the graft junction. However, auxin transport and signaling, DNA replication, and xylem and phloem pattern formation were restricted to the scion, whereas the cytokinin-activated signaling pathway and the cellular response to sucrose starvation was restricted to the rootstock. At 24−72 HAG, cell division occurred above the graft junction, and photosynthesis-related pathways were activated below the graft junction. The levels of auxin and cytokinin reached their maxima above and below the graft junction at 12 HAG, respectively. Exogenous application of certain concentrations of IAA and 6-BA will promote xylem and phloem transport capacity. The current work has analyzed the stage-specific events and hub genes during the developmental progression of tomato grafting. We found that auxin and cytokinin levels respond to grafting, above and below the graft junction, respectively, to promote the formation of xylem and phloem patterning. In addition, the accumulation of auxin above the graft junction induced cells to prepare for mitosis and promoted the formation of callus. In short, our work provides an important reference for theoretical research and production application of tomato grafting in the future."
Authors: Matthew J. van Voorthuizen, Jaroslav Nisler, Jiancheng Song, Lukáš Spíchal and Paula E. Jameson.
Plants (2021)
Abstract: "Modifying the cytokinin content in plants is a means of improving plant productivity. Here, we report the development and biological activity of compound TD-K (1-(furan-2-ylmethyl)-3-(1,2,3-thiadiazol-5-yl)urea) which is related to thidiazuron. TD-K—which exhibited extremely high antisenescence activity in the wheat leaf bioassay—and INCYDE (2-chloro-6-(3-methoxyphenyl)aminopurine)—a plant growth regulator reported to inhibit cytokinin oxidase/dehydrogenase (CKX), an enzyme involved in the degradation of the plant hormone cytokinin—were selected for investigation of their effects on the model plant Rapid Cycling Brassica rapa (RCBr). We monitored the expression of BrCKX and isopentenyl transferase (BrIPT), which codes for the key cytokinin biosynthesis enzyme, in developing leaves following INCYDE and TD-K application. Growth room experiments revealed that INCYDE increased RCBr seed yield per plant, but only when applied multiple times and when grown in 5 mM KNO3. Expression in control leaves showed transient, high levels of expression of BrCKX and BrIPT at true leaf appearance. Following INCYDE application, there was a rapid and strong upregulation of BrCKX3, and a transient downregulation of BrIPT1 and BrIPT3. Interestingly, the upregulation of BrCKX3 persisted in a milder form throughout the course of the experiment (16 days). TD-K also upregulated BrCKX3. However, in contrast to INCYDE, this effect disappeared after two days. These results suggest that both compounds (CKX inhibitor and cytokinin TD-K) influenced cytokinin homeostasis in RCBr leaves, but with different mechanisms."
Authors: Sachiko Tanaka, Kayo Hashimoto, Yuuki Kobayashi, Koji Yano, Taro Maeda, Hiromu Kameoka, Tatsuhiro Ezawa, Katsuharu Saito, Kohki Akiyama and Masayoshi Kawaguchi.
bioRxiv (2020)
Abstract: "Arbuscular mycorrhizal (AM) symbiosis is a mutually beneficial interaction between fungi and land plants and promotes global phosphate cycling in terrestrial ecosystems. AM fungi are recognised as obligate symbionts that require root colonisation to complete a life cycle involving the production of propagules, asexual spores. Recently it has been shown that Rhizophagus irregularis can produce infection-competent secondary spores asymbiotically by adding a fatty acid, palmitoleic acid. Further, asymbiotic growth can be supported using myristate as a carbon and energy source for their asymbiotic growth to increase fungal biomass. However, spore production and the ability of these spores to colonise host roots were still limited compared to co-culture of the fungus with plant roots. Here we show that a combination of two plant hormones, strigolactone and methyl jasmonate, induces production of a large number of infection-competent spores in asymbiotic cultures of Rhizophagus clarus HR1 in the presence of myristate and organic nitrogen. Inoculation of asymbiotically-generated spores promoted the growth of Welsh onions, as observed for spores produced by symbiotic culture system. Our findings provide a foundation for elucidation of hormonal control of the fungal life cycle and development of new inoculum production schemes."
Authors: Chi Zhang, Minta Chaiprasongsuk, Andre S. Chanderbali, Xinlu Chen, Jianyu Fu, Douglas E. Soltis and Feng Chen.
Plant Direct (2020)
Abstract: " Gibberellins (GAs) are a major class of plant hormones that regulates diverse developmental programs. Both acquiring abilities to synthesize GAs and evolving divergent GA receptors have been demonstrated to play critical roles in the evolution of land plants. In contrast, little is understood regarding the role of GA‐inactivating mechanisms in plant evolution. Here we report on the origin and evolution of GA methyltransferases (GAMTs), enzymes that deactivate GAs by converting bioactive GAs to inactive GA methylesters. Prior to this study, GAMT genes, which belong to the SABATH family, were known only from Arabidopsis. Through systematic searches for SABATH genes in the genomes of 260 sequenced land plants and phylogenetic analyses, we have identified a putative GAMT clade specific to seed plants. We have further demonstrated that both gymnosperm and angiosperm representatives of this clade encode active methyltransferases for GA methylation, indicating that they are functional orthologs of GAMT. In seven selected seed plants, GAMT genes were mainly expressed in flowers and/or seeds, indicating a conserved biological role in reproduction. GAMT genes are represented by a single copy in most species, if present, but multiple copies mainly produced by whole genome duplications have been retained in Brassicaceae. Surprisingly, more than 2/3 of the 248 flowering plants examined here lack GAMT genes, including all species of Poales (e.g., grasses), Fabales (legumes), and the large Superasterid clade of eudicots. With these observations, we discuss the significance of GAMT origination, functional conservation and diversification, and frequent loss during the evolution of flowering plants."
Authors: Cristina Martínez Andújar, Ascensión Martínez-Pérez, Alfonso Albacete Moreno, Purificación A. Martínez-Melgarejo, Ian Dodd, Andrew J. Thompson, Almudena Ferrández-Ayela, Jose Manuel Perez-Perez, Miriam Gifford and Francisco Pérez Alfocea.
Authorea (2020)
Abstract: "To determine whether root-supplied ABA alleviates saline stress, tomato (Solanum lycopersicum L. cv. Sugar Drop) was grafted onto two independent lines overexpressing the SlNCED1 (9-cis-epoxycarotenoid dioxygenase) gene (NCED OE) and wild type rootstocks. After 200 days of salinity irrigation (EC = 3.5 dS m-1), plants with NCED OE rootstocks had 30% higher fruit yield, but root biomass and lateral root development was reduced. Although NCED OE rootstocks upregulated ABA-signalling (AREB, ATHB12), ethylene-related (ACCs, ERFs), aquaporin (PIPs) and stress-related (TAS14, KIN, LEA) genes, downregulation of PYL ABA receptors and signalling components (WRKYs), ethylene synthesis (ACOs) and auxin responsive factors occurred. Elevated SlNCED1 expression enhanced ABA levels in reproductive tissue while ABA catabolites accumulated in leaf and xylem sap suggesting homeostatic mechanisms. NCED OE also reduced xylem cytokinin transport to the shoot and stimulated foliar 2-isopentenyl adenine (iP) accumulation and phloem transport. Moreover, increased xylem gibberellin GA3 levels in growing fruit trusses was associated with enhanced reproductive growth. Improved photosynthesis without changes in stomatal conductance was consistent with hormone-mediated alteration of leaf growth and mesophyll structure, which combined with lower assimilate requirement in the roots and systemic changes in hormone balances could explain enhanced vigour, reproductive growth and yield under saline stress."
Authors: Dawei Zhang, Wenrong Tan, Feng Yang, Qing Han, Xingguang Deng, Hongqing Guo, Baohui Liu, Yanhai Yin and Honghui Lin.
Developmental Cell (2021)
Editor's view: BR signaling is known to inhibit photomorphogenesis, including chloroplast development, but the mechanism underlying this is not well known. Zhang et al. identify a BIN2-GLK1 signaling module that integrates BR and light to precisely fine-tune chloroplast development in response to light conditions.
Highlights: • BR signaling inhibits chloroplast development • BIN2 interacts with and phosphorylates GLKs in nuclei • Phosphorylation by BIN2 promotes the stability and transcriptional activity of GLK1 • GLK1 phosphorylation during light conditions positively regulates cotyledon greening
Abstract: "Arabidopsis GLYCOGEN SYNTHASE KINASE 3 (GSK3)-like kinases play various roles in plant development, including chloroplast development, but the underlying molecular mechanism is not well defined. Here, we demonstrate that transcription factors GLK1 and GLK2 interact with and are phosphorylated by the BRASSINOSTEROID insensitive2 (BIN2). The loss-of-function mutant of BIN2 and its homologs, bin2-3 bil1 bil2, displays abnormal chloroplast development, whereas the gain-of-function mutant, bin2-1, exhibits insensitivity to BR-induced de-greening and reduced numbers of thylakoids per granum, suggesting that BIN2 positively regulates chloroplast development. Furthermore, BIN2 phosphorylates GLK1 at T175, T238, T248, and T256, and mutations of these phosphorylation sites alter GLK1 protein stability and DNA binding and impair plant responses to BRs/darkness. On the other hand, BRs and darkness repress the BIN2-GLK module to enhance BR/dark-mediated de-greening and impair the formation of the photosynthetic apparatus. Our results thus provide a mechanism by which BRs modulate photomorphogenesis and chloroplast development."
Authors: Qian‐Qian Li, Zhan Zhang, Ya‐Ling Wang, Li‐Yuan Zhong, Zhen‐Fei Chao, Yi‐Qun Gao, Mei‐Ling Han, Lin Xu and Dai‐Yin Chao.
The Plant Journal (2021)
Abstract: "Adventitious roots (ARs) are an important root type for plants and display a high phenotypic plasticity in response to different environmental stimuli. Previous studies found that dark‐light transition can trigger AR formation from the hypocotyl of etiolated Arabidopsis thaliana, which was used as model for identification of regulators of AR biogenesis. However, the central regulatory machinery for darkness‐induced hypocotyl AR (HAR) remains elusive. Here, we report that photoreceptors suppress HAR biogenesis through regulating the molecular module essential for lateral roots. We found that hypocotyls embedded in soil or in continuous darkness are able to develop HARs, wherein photoreceptors act as negative regulators. Distinct from wound‐induced ARs that require WOX11 and WOX12, darkness‐induced HARs are fully dependent on ARF7, ARF19, WOX5/7 and LBD16. Further studies established that PHYB interacts with IAA14, ARF7 and ARF9. The interactions stabilize IAA14 and inhibit the transcriptional activities of ARF7 and ARF19 and thus suppress biogenesis of darkness‐induced HARs. This finding not only revealed the central machinery controlling HAR biogenesis but also illustrated that AR formation could be initiated by multiple pathways."
Author: Peter Hedden.
Plant and Cell Physiology (2020)
Abstract: "Gibberellins are produced by all vascular plants and several fungal and bacterial species that associate with plants as pathogens or symbionts. In the 60 years since the first experiments on the biosynthesis of gibberellic acid in the fungus Fusarium fujikuroi, research on gibberellin biosynthesis has advanced to provide detailed information on the pathways, biosynthetic enzymes and their genes in all three kingdoms, in which the production of the hormones evolved independently. Gibberellins function as hormones in plants, affecting growth and differentiation in organs in which their concentration is very tightly regulated. Current research in plants is focused particularly on the regulation of gibberellin biosynthesis and inactivation by developmental and environmental cues, and there is now considerable information on the molecular mechanisms involved in these processes. There have also been recent advances in understanding gibberellin transport and distribution and their relevance to plant development. This review describes our current understanding of gibberellin metabolism and its regulation, highlighting the more recent advances in this field."
Authors: Hyeona Hwang, Hwa-Yong Lee, Hojin Ryu and Hyunwoo Cho.
International Journal of Molecular Sciences (2020)
Abstract: "Brassinosteroids (BRs) play crucial roles in the physiology and development of plants. In the model plant Arabidopsis, BR signaling is initiated at the level of membrane receptors, BRASSINOSTEROIDS INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) complex, thus activating the transcription factors (TFs) BRASSINAZOLE RESISTANT 1/BRI1-EMS-SUPPRESSOR 1 (BZR1/BES1) to coordinate BR responsive genes. BRASSINOSTEROIDS INSENSITIVE 2 (BIN2), glycogen synthase kinase 3 (GSK3) like-kinase, negatively regulates BZR1/BES1 transcriptional activity through phosphorylation-dependent cytosolic retention and shuttling. However, it is still unknown whether this mechanism is conserved in Panax ginseng C. A. Mayer, a member of the Araliaceae family, which is a shade-tolerant perennial root crop. Despite its pharmacological and agricultural importance, the role of BR signaling in the development of P. ginseng and characterization of BR signaling components are still elusive. In this study, by utilizing the Arabidopsis bri1 mutant, we found that ectopic expression of the gain of function form of PgBZR1 (Pgbzr1-1D) restores BR deficiency. In detail, ectopic expression of Pgbzr1-1D rescues dwarfism, defects of floral organ development, and hypocotyl elongation of bri1-5, implying the functional conservation of PgBZR1 in P. ginseng. Interestingly, brassinolide (BL) and BRs biosynthesis inhibitor treatment in two-year-old P. ginseng storage root interferes with and promotes, respectively, secondary growth in terms of xylem formation. Altogether, our results provide new insight into the functional conservation and potential diversification of BR signaling and response in P. ginseng."
Authors: Jianyang Liu, Yanning Wang and Youfa Cheng.
The Plant Journal (2020)
Abstract: "The highly conserved endosomal sorting complex required for transport (ESCRT) pathway plays critical roles in endosomal sorting of ubiquitinated plasma membrane proteins for degradation. However, the functions of many components of the ESCRT machinery in plants remain unsolved. Here we show that the ESCRT‐I subunits VPS28A and VPS28B are functionally redundant and required for embryonic development in Arabidopsis. We conducted a screen for genetic enhancers of pid, which is defective in auxin signaling and transport. We isolated a no‐‐cotyledon in pid 104 (ncp104) mutant, which failed to develop cotyledons in a pid background. We discovered that ncp104 was a unique recessive gain‐of‐function allele of vps28a. VPS28A and VPS28B were expressed during embryogenesis and the proteins were localized to the trans‐Golgi network/early endosome and post‐Golgi/endosomal compartments, consistent with their functions in endosomal sorting and embryogenesis. The single vps28a and vps28b loss‐of‐function mutants did not display obvious developmental defects, but their double mutants showed abnormal cell division patterns and were arrested at the globular embryo stage. The vps28a vps28b double mutants showed altered auxin responses, disrupted PIN1‐GFP expression patterns, and abnormal PIN1‐GFP accumulation in small aberrant vacuoles. The ncp104 mutation may cause the VPS28A protein to become unstable and/or toxic. Taken together, our findings demonstrate that the ESCRT‐I components VPS28A and VPS28B redundantly play essential roles in vacuole formation, endosomal sorting of plasma membrane proteins, and auxin‐mediated plant development."
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Authors: by Eva Pokorná,Tomáš Hluska, Petr Galuszka, H. Tucker Hallmark, Petre I. Dobrev, Lenka Záveská Drábková, Tomáš Filipi, Katarína Holubová, Ondřej Plíhal, Aaron M. Rashotte, Roberta Filepová, Jiří Malbeck, Ondřej Novák, Lukáš Spíchal, Břetislav Brzobohatý, Pavel Mazura, Lenka Zahajská and Václav Motyka.
Biomolecules (2021)
Abstract: "Cytokinins (CKs) are a class of phytohormones affecting many aspects of plant growth and development. In the complex process of CK homeostasis in plants, N-glucosylation represents one of the essential metabolic pathways. Its products, CK N7- and N9-glucosides, have been largely overlooked in the past as irreversible and inactive CK products lacking any relevant physiological impact. In this work, we report a widespread distribution of CK N-glucosides across the plant kingdom proceeding from evolutionary older to younger plants with different proportions between N7- and N9-glucosides in the total CK pool. We show dramatic changes in their profiles as well as in expression levels of the UGT76C1 and UGT76C2 genes during Arabidopsis ontogenesis. We also demonstrate specific physiological effects of CK N-glucosides in CK bioassays including their antisenescent activities, inhibitory effects on root development, and activation of the CK signaling pathway visualized by the CK-responsive YFP reporter line, TCSv2::3XVENUS. Last but not least, we present the considerable impact of CK N7- and N9-glucosides on the expression of CK-related genes in maize and their stimulatory effects on CK oxidase/dehydrogenase activity in oats. Our findings revise the apparent irreversibility and inactivity of CK N7- and N9-glucosides and indicate their involvement in CK evolution while suggesting their unique function(s) in plants."
Authors: Mohammad Saidur Rhaman, Shahin Imran, Farjana Rauf, Mousumi Khatun, Carol C. Baskin, Yoshiyuki Murata and Mirza Hasanuzzaman.
Plants (2020)
Abstract: "Plants are often exposed to abiotic stresses such as drought, salinity, heat, cold, and heavy metals that induce complex responses, which result in reduced growth as well as crop yield. Phytohormones are well known for their regulatory role in plant growth and development, and they serve as important chemical messengers, allowing plants to function during exposure to various stresses. Seed priming is a physiological technique involving seed hydration and drying to improve metabolic processes prior to germination, thereby increasing the percentage and rate of germination and improving seedling growth and crop yield under normal and various biotic and abiotic stresses. Seed priming allows plants to obtain an enhanced capacity for rapidly and effectively combating different stresses. Thus, seed priming with phytohormones has emerged as an important tool for mitigating the effects of abiotic stress. Therefore, this review discusses the potential role of priming with phytohormones to mitigate the harmful effects of abiotic stresses, possible mechanisms for how mitigation is accomplished, and roles of priming on the enhancement of crop production."
Authors: Joohyun Kang, Youngsook Lee and Enrico Martinoia.
In: Progress in Botany (2021)
Abstract: "Abscisic acid (ABA) is generally known as the plant stress hormone. Functioning in a wide range of environmental responses, ABA plays a major role in drought tolerance. In addition to inducing stomatal closure during drought stress, ABA promotes suberization of the exodermis and endodermis, which reduces water loss from the root. Furthermore, ABA increases freezing tolerance and has a complex, but not completely understood, role in plant–pathogen interactions. ABA also functions in plant development; for example, ABA is a central player in maintaining seed dormancy. Whereas the enzymatic steps of ABA biosynthesis have been known for some time, our knowledge of ABA receptors and transporters is quite recent. This is due, at least partially, to redundancy among members of both the ABA receptor and transporter families. Many transporters from different transporter families cooperate to transport ABA. The weak but distinct phenotypes described for the different loss-of-function mutants indicate that each of these transporters plays a specific role and, at least under a given condition or in a specific tissue, they are not completely redundant. However, for each function described so far, delivery of ABA at the target site requires the activity of several different ABA transporters. This strategy may ensure that ABA is transported to the correct target even if one of the transporters is nonfunctional or that plants can transport ABA under a given condition via several routes."
Authors: Jiao Wang, Chenfei Zheng, Xiangqi Shao, Zhangjian Hu, Jianxin Li, Ping Wang, Anran Wang, Jingquan Yu and Kai Shi.
Horticultural Research (2020)
Abstract: "With global climate change, plants are frequently being exposed to various stresses, such as pathogen attack, drought, and extreme temperatures. Transcription factors (TFs) play crucial roles in numerous plant biological processes; however, the functions of many tomato (Solanum lycopersicum L.) TFs that regulate plant responses to multiple stresses are largely unknown. Here, using an RNA-seq approach, we identified SlNAP1, a NAC TF-encoding gene, which was strongly induced by various stresses. By generating SlNAP1 transgenic lines and evaluating their responses to biotic and abiotic stresses in tomato, we found that SlNAP1-overexpressing plants showed significantly enhanced defense against two widespread bacterial diseases, leaf speck disease, caused by Pseudomonas syringae pv. tomato (Pst) DC3000, and root-borne bacterial wilt disease, caused by Ralstonia solanacearum. In addition, SlNAP1 overexpression dramatically improved drought tolerance in tomato. Although the SlNAP1-overexpressing plants were shorter than the wild-type plants during the early vegetative stage, eventually, their fruit yield increased by 10.7%. Analysis of different hormone contents revealed a reduced level of physiologically active gibberellins (GAs) and an increased level of salicylic acid (SA) and abscisic acid (ABA) in the SlNAP1-overexpressing plants. Moreover, EMSAs and ChIP-qPCR assays showed that SlNAP1 directly activated the transcription of multiple genes involved in GA deactivation and both SA and ABA biosynthesis. Our findings reveal that SlNAP1 is a positive regulator of the tomato defense response against multiple stresses and thus may be a potential breeding target for improving crop yield and stress resistance."
Author: W. Robert Williams.
Plant Signaling & Behavior (2021)
Abstract: "Structural components of second messenger signaling (nucleotides and associated enzyme systems) within plant and animal cells have more in common than the hormones that initiate metabolic and functional changes. Neurotransmitters and hormones of mammalian pharmacologic classes relate to purine nucleotides in respect of chemical structure and the molecular changes they initiate. This study compares the molecular structures of purine nucleotides with compounds from the abscisic acid, auxin, brassinosteroid, cytokinin, gibberellin, and jasmonate classes by means of a computational program. The results illustrate how phytohomones relate to each other through the structures of nucleotides and cyclic nucleotides. Molecular similarity within the phytohormone structures relates to synergism, antagonism and the modulation of nucleotide function that regulates germination and plant development. As with the molecular evolution of mammalian hormones, cell signaling and cross-talk within the phytohormone classes is purine nucleotide centered."
Authors: Fernanda Garrido-Vargas, Tamara Godoy, Ricardo Tejos and José Antonio O’Brien.
International Journal of Molecular Sciences (2020)
Abstract: "Soil salinity is a key problem for crop production worldwide. High salt concentration in soil negatively modulates plant growth and development. In roots, salinity affects the growth and development of both primary and lateral roots. The phytohormone auxin regulates various developmental processes during the plant’s life cycle, including several aspects of root architecture. Auxin signaling involves the perception by specialized receptors which module several regulatory pathways. Despite their redundancy, previous studies have shown that their functions can also be context-specific depending on tissue, developmental or environmental cues. Here we show that the over-expression of Auxin Signaling F-Box 3 receptor results in an increased resistance to salinity in terms of root architecture and germination. We also studied possible downstream signaling components to further characterize the role of auxin in response to salt stress. We identify the transcription factor SZF1 as a key component in auxin-dependent salt stress response through the regulation of NAC4. These results give lights of an auxin-dependent mechanism that leads to the modulation of root system architecture in response to salt identifying a hormonal cascade important for stress response."
Authors: H. Tucker Hallmark and Aaron M. Rashotte.
Plant Direct (2020)
Abstract: "Cytokinins (CKs) are well‐known as a class of phytohormones capable of delaying senescence in detached leaves. However, CKs are often treated as a monolithic group of compounds even though dozens of CK species are present in plants with varied degrees of reported biological activity. One specific type of CK, isopentenyladenine base (iP), has been demonstrated as having roles in delaying leaf senescence, inhibition of root growth, and promoting shoot regeneration. However, its N‐glucosides isopentenyladenine‐7‐ and ‐9‐glucoside (iP7G, iP9G) have remained understudied and thought of as inactive cytokinins for several decades, despite their relatively high concentrations in plants such as the model species Arabidopsis thaliana. Here we show that iP and one of its glucosides, iP9G, are capable of delaying senescence in leaves, though the glucosides having little to no activity in other bioassays. Additionally, we performed the first transcriptomic study of iP‐delayed cotyledon senescence which shows that iP is capable of upregulating photosynthetic genes and downregulating catabolic genes in detached cotyledons. Transcriptomic analysis also shows iP9G has limited effects on gene expression, but that the few affected genes are CK‐related and are similar to those seen from iP effects during senescence as seen for the type‐A response regulator ARR6. These findings suggest that iP9G functions as an active CK during senescence."
Authors: Zhiyuan Bian, Huanhuan Gao and Chongying Wang.
International Journal of Molecular Sciences (2020)
Abstract: "The NAC (NAM, ATAF1/2, and CUC2) family of proteins is one of the largest plant-specific transcription factor (TF) families and its members play varied roles in plant growth, development, and stress responses. In recent years, NAC TFs have been demonstrated to participate in crop-pathogen interactions, as positive or negative regulators of the downstream defense-related genes. NAC TFs link signaling pathways between plant hormones, including salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA), or other signals, such as reactive oxygen species (ROS), to regulate the resistance against pathogens. Remarkably, NAC TFs can also contribute to hypersensitive response and stomatal immunity or can be hijacked as virulence targets of pathogen effectors. Here, we review recent progress in understanding the structure, biological functions and signaling networks of NAC TFs in response to pathogens in several main food crops, such as rice, wheat, barley, and tomato, and explore the directions needed to further elucidate the function and mechanisms of these key signaling molecules."
Authors: Galina Smolikova, Tatiana Leonova, Natalia Vashurina, Andrej Frolov and Sergei Medvedev.
International Journal of Molecular Sciences (2020)
Abstract: "Desiccation tolerance appeared as the key adaptation feature of photoautotrophic organisms for survival in terrestrial habitats. During the further evolution, vascular plants developed complex anatomy structures and molecular mechanisms to maintain the hydrated state of cell environment and sustain dehydration. However, the role of the genes encoding the mechanisms behind this adaptive feature of terrestrial plants changed with their evolution. Thus, in higher vascular plants it is restricted to protection of spores, seeds and pollen from dehydration, whereas the mature vegetative stages became sensitive to desiccation. During maturation, orthodox seeds lose up to 95% of water and successfully enter dormancy. This feature allows seeds maintaining their viability even under strongly fluctuating environmental conditions. The mechanisms behind the desiccation tolerance are activated at the late seed maturation stage and are associated with the accumulation of late embryogenesis abundant (LEA) proteins, small heat shock proteins (sHSP), non-reducing oligosaccharides, and antioxidants of different chemical nature. The main regulators of maturation and desiccation tolerance are abscisic acid and protein DOG1, which control the network of transcription factors, represented by LEC1, LEC2, FUS3, ABI3, ABI5, AGL67, PLATZ1, PLATZ2. This network is complemented by epigenetic regulation of gene expression via methylation of DNA, post-translational modifications of histones and chromatin remodeling. These fine regulatory mechanisms allow orthodox seeds maintaining desiccation tolerance during the whole period of germination up to the stage of radicle protrusion. This time point, in which seeds lose desiccation tolerance, is critical for the whole process of seed development."
Authors: Hideki Yoshida, Masatoshi Nakajima and Makoto Matsuoka
Plant and Cell Physiology (2020)
Excerpts: "More than 100 years ago, a Japanese plant pathologist reported that the ‘foolish seedling disease’ of rice was caused by fungal infection (Hori 1898); this was the first report dealing with gibberellin (GA). Because this disease induced severe problems for rice cultivation, Japanese scientists intensively studied its cause. They eventually found that such abnormal growth was caused by a chemical called GA, after its fungal source Gibberella fujikuroi (Yabuta 1935)."
"Five of the articles in this special issue focus on GA metabolism. With over a half-century of research, GA metabolic pathways in plants, fungi and bacteria are now thought to be well understood."
"This issue also contains three review papers focusing on more specific evolutionary features of GA metabolism."
"This issue also contains three review papers to describe and discuss the mechanisms underlying the regulation of GA action in terms of epigenetic, posttranscriptional and posttranslational regulation."
Authors: Yunhua Xiao, Junwen Zhang, Guiyuan Yu, Xuedan Lu, Wentao Mei, Huabing Deng, Guilian Zhang, Guihua Chen, Chengcai Chu, Hongning Tong and Wenbang Tang.
Frontiers in Plant Science (2020)
Abstract: "Cytokinins (CKs) are a class of phytohormones playing essential roles in various biological processes. However, the mechanisms underlying CK transport as well as its function in plant growth and development are far from being fully elucidated. Here, we characterize the function of PURINE PERMEASE1 (OsPUP1) in rice (Oryza sativa L.). OsPUP1 was predominantly expressed in the root, particularly in vascular cells, and CK treatment can induce its expression. Subcellular localization analysis showed that OsPUP1 was predominantly localized to the endoplasmic reticulum (ER). Overexpression of OsPUP1 resulted in growth defect of various aerial tissues, including decreased leaf length, plant height, grain weight, panicle length, and grain number. Hormone profiling revealed that the CK content was decreased in the shoot of OsPUP1-overexpressing seedling, but increased in the root, compared with the wild type. The CK content in the panicle was also decreased. Quantitative reverse transcription-PCR (qRT-PCR) analysis using several CK type-A response regulators (OsRRs) as the marker genes suggested that the CK response in the shoot of OsPUP1-overexpressing seedling is decreased compared to the wild type when CKs are applied to the root. Genetic analysis revealed that BG3/OsPUP4, a putative plasma membrane-localized CK transporter, overcomes the function of OsPUP1. We hypothesize that OsPUP1 might be involved in importing CKs into ER to unload CKs from the vascular tissues be involved in importing CKs into ER to unload CKs from the vascular tissues by cell-to-cell transport."
Authors: Tianyu Xia, Hongqi Chen, Sujun Dong, Zeyang Ma, Haibo Ren, Xudong Zhu, Xiaohua Fang and Fan Chen.
The Plant Journal (2020)
Abstract: "Two branching strategies are exhibited in crops: enhanced apical dominance, as in maize; or weak apical dominance, as in rice. However, the underlying mechanism of weak apical dominance remains elusive. OsWUS, an ortholog of Arabidopsis WUSCHEL (WUS) in rice, is required for tiller development. In this study, we identified and functionally characterized a low‐tillering mutant decreased culm number 1 (dc1) that resulted from loss‐of‐function of OsWUS. The dc1 tiller buds are viable but repressed by the main culm apex, leading to stronger apical dominance than that of the wild‐type (WT). Auxin response is enhanced in the dc1 mutant, and knocking out the auxin action‐associated gene ABERRANT SPIKELET AND PANICLE 1 (ASP1) de‐repressed growth of the tiller buds in the dc1 mutant, suggesting that OsWUS and ASP1 are both involved in outgrowth of the rice tiller bud. Decapitation triggers higher contents of cytokinins in the shoot base of the dc1 mutant compared with those in the WT, and exogenous application of cytokinin is not sufficient for sustained growth of the dc1 tiller bud. Transcriptome analysis indicated that expression levels of transcription factors putatively bound by ORYZA SATIVA HOMEOBOX 1 (OSH1) are changed in response to decapitation and display a greater fold change in the dc1 mutant than that in the WT. Collectively, these findings reveal an important role of OsWUS in tiller bud growth by influencing apical dominance, and provide the basis for an improved understanding of tiller bud development in rice."
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