A gene regulatory network controlled by the NAC transcription factor ANAC092/AtNAC2/ORE1 during salt-promoted senescence

Molecular Evolution of RAMOSA1 (RA1) in Land Plants

RAMOSA1 (RA1) is a Cys2-His2-type (C2H2) zinc finger transcription factor that controls plant meristem fate and identity and has played an important role in maize domestication. Despite its importance, the origin of RA1 is unknown, and the evolution in plants is only partially understood. In this paper, we present a well-resolved phylogeny based on 73 amino acid sequences from 48 embryophyte species. The recovered tree topology indicates that, during grass evolution, RA1 arose from two consecutive SUPERMAN duplications, resulting in three distinct grass sequence lineages: RA1-like A, RA1-like B, and RA1; however, most of these copies have unknown functions. Our findings indicate that RA1 and RA1-like play roles in the nucleus despite lacking a traditional nuclear localization signal. Here, we report that copies diversified their coding region and, with it, their protein structure, suggesting different patterns of DNA binding and protein-protein interaction. In addition, each of the retained copies diversified regulatory elements along their promoter regions, indicating differences in their upstream regulation. Taken together, the evidence indicates that the RA1 and RA1-like gene families in grasses underwent subfunctionalization and neofunctionalization enabled by gene duplication.

PeNAC67-PeKAN2-PeSCL23 and B-class MADS-box transcription factors synergistically regulate the specialization process from petal to lip in Phalaenopsis equestris

The molecular basis of orchid flower development involves a specific regulatory program in which MADS-box transcription factors play a central role. The recent 'perianth code' model hypothesizes that two types of higher-order heterotetrameric complexes, namely SP complex and L complex, play pivotal roles in the orchid perianth organ formation. Therefore, we explored their roles and searched for other components of the regulatory network.Through the combined analysis for transposase-accessible chromatin with high-throughput sequencing and RNA sequencing of the lip-like petal and lip from Phalaenopsis equestris var.trilip, transcription factor-(TF) genes involved in lip development were revealed. PeNAC67 encoding a NAC-type TF and PeSCL23 encoding a GRAS-type TF were differentially expressed between the lip-like petal and the lip. PeNAC67 interacted with and stabilized PeMADS3, which positively regulated the development of lip-like petal to lip. PeSCL23 and PeNAC67 competitively bound with PeKAN2 and positively regulated the development of lip-like petal to petal by affecting the level of PeMADS3. PeKAN2 as an important TF that interacts with PeMADS3 and PeMADS9 can promote lip development. These results extend the 'perianth code' model and shed light on the complex regulation of orchid flower development.

PSEUDO-ETIOLATION IN LIGHT proteins reduce greening by binding GLK transcription factors

Knocking out genes encoding proteins that downregulate the accumulation of pigments may lead to increases in crop quality and yield. PSEUDO-ETIOLATION IN LIGHT 1 (PEL1) downregulates the accumulation of carotenoids in carrot and chlorophyll in Arabidopsis and rice and may inhibit GOLDEN 2-LIKE (GLK) transcription factors. PEL1 belongs to a previously unstudied gene family found only in plants. We used CRISPR/Cas9 technology to knock out each member of the 4-member PEL gene family and both GLK genes in Arabidopsis. In pel mutants, chlorophyll levels were elevated in seedlings; after flowering, chloroplasts increased in size, and anthocyanin levels increased. Although the chlorophyll-deficient phenotype of glk1 glk2 was epistatic to pel1 pel2 pel3 pel4 in most of our experiments, glk1 glk2 was not epistatic to pel1 pel2 pel3 pel4 for the accumulation of anthocyanins in most of our experiments. The pel alleles attenuated growth, altered the accumulation of nutrients in seeds, disrupted an abscisic acid-inducible inhibition of seedling growth response that promotes drought tolerance, and affected the expression of genes associated with diverse biological functions, such as stress responses, cell wall metabolism hormone responses, signaling, growth, and the accumulation of phenylpropanoids and pigments. We found that PEL proteins specifically bind 6 transcription factors that influence the accumulation of anthocyanins, GLK2, and the carboxy termini of GLK1 and Arabidopsis thaliana myeloblastosis oncogene homolog 4 (AtMYB4). Our data indicate that the PEL proteins influence the accumulation of chlorophyll and many other processes, possibly by inhibiting GLK transcription factors and via other mechanisms, and that multiple mechanisms downregulate chlorophyll content.

Differential leaf flooding resilience in Arabidopsis thaliana is controlled by ethylene signaling-activated and age-dependent phosphorylation of ORESARA1

The phytohormone ethylene is a major regulator of plant adaptive responses to flooding. In flooded plant tissues, ethylene quickly increases to high concentrations owing to its low solubility and diffusion rates in water. Ethylene accumulation in submerged plant tissues makes it a reliable cue for triggering flood acclimation responses, including metabolic adjustments to cope with flood-induced hypoxia. However, persistent ethylene accumulation also accelerates leaf senescence. Stress-induced senescence hampers photosynthetic capacity and stress recovery. In submerged Arabidopsis, senescence follows a strict age-dependent pattern starting with the older leaves. Although mechanisms underlying ethylene-mediated senescence have been uncovered, it is unclear how submerged plants avoid indiscriminate breakdown of leaves despite high systemic ethylene accumulation. We demonstrate that although submergence triggers leaf-age-independent activation of ethylene signaling via EIN3 in Arabidopsis, senescence is initiated only in old leaves. EIN3 stabilization also leads to overall transcript and protein accumulation of the senescence-promoting transcription factor ORESARA1 (ORE1) in both old and young leaves during submergence. However, leaf-age-dependent senescence can be explained by ORE1 protein activation via phosphorylation specifically in old leaves, independent of the previously identified age-dependent control of ORE1 via miR164. A systematic analysis of the roles of the major flooding stress cues and signaling pathways shows that only the combination of ethylene and darkness is sufficient to mimic submergence-induced senescence involving ORE1 accumulation and phosphorylation. Hypoxia, most often associated with flooding stress in plants, appears to have no role in these processes. Our results reveal a mechanism by which plants regulate the speed and pattern of senescence during environmental stresses such as flooding. Age-dependent ORE1 activity ensures that older, expendable leaves are dismantled first, thus prolonging the life of younger leaves and meristematic tissues that are vital to whole-plant survival.

Functions of Phytochrome Interacting Factors (PIFs) in Adapting Plants to Biotic and Abiotic Stresses

Plants possess the remarkable ability to sense detrimental environmental stimuli and launch sophisticated signal cascades that culminate in tailored responses to facilitate their survival, and transcription factors (TFs) are closely involved in these processes. Phytochrome interacting factors (PIFs) are among these TFs and belong to the basic helix-loop-helix family. PIFs are initially identified and have now been well established as core regulators of phytochrome-associated pathways in response to the light signal in plants. However, a growing body of evidence has unraveled that PIFs also play a crucial role in adapting plants to various biological and environmental pressures. In this review, we summarize and highlight that PIFs function as a signal hub that integrates multiple environmental cues, including abiotic (i.e., drought, temperature, and salinity) and biotic stresses to optimize plant growth and development. PIFs not only function as transcription factors to reprogram the expression of related genes, but also interact with various factors to adapt plants to harsh environments. This review will contribute to understanding the multifaceted functions of PIFs in response to different stress conditions, which will shed light on efforts to further dissect the novel functions of PIFs, especially in adaption to detrimental environments for a better survival of plants.

Lateral root primordium: Formation, influencing factors and regulation

Roots are the primary determinants of water and nutrient uptake by plants. The structure of roots is largely determined by the repeated formation of new lateral roots (LR). A new lateral root primordium (LRP) is formed between the beginning and appearance of LR, which defines the organization and function of LR. Therefore, proper LRP morphogenesis is a crucial process for lateral root formation. The development of LRP is regulated by multiple factors, including hormone and environmental signals. Roots integrate signals and regulate growth and development. At the molecular level, many genes regulate the growth and development of root organs to ensure stable development plans, while also being influenced by various environmental factors. To gain a better understanding of the LRP formation and its influencing factors, this study summarizes previous research. The cell cycle involved in LRP formation, as well as the roles of ROS, auxin, other auxin-related plant hormones, and genetic regulation, are discussed in detail. Additionally, the effects of gravity, mechanical stress, and cell death on LRP formation are explored. Throughout the text unanswered or poorly understood questions are identified to guide future research in this area.

Phosphorylation of Thr-225 and Ser-262 on ERD7 Promotes Age-Dependent and Stress-Induced Leaf Senescence through the Regulation of Hydrogen Peroxide Accumulation in Arabidopsis thaliana

As the final stage of leaf development, leaf senescence is affected by a variety of internal and external signals including age and environmental stresses. Although significant progress has been made in elucidating the mechanisms of age-dependent leaf senescence, it is not clear how stress conditions induce a similar process. Here, we report the roles of a stress-responsive and senescence-induced gene, ERD7 (EARLY RESPONSIVE TO DEHYDRATION 7), in regulating both age-dependent and stress-induced leaf senescence in Arabidopsis. The results showed that the leaves of erd7 mutant exhibited a significant delay in both age-dependent and stress-induced senescence, while transgenic plants overexpressing the gene exhibited an obvious accelerated leaf senescence. Furthermore, based on the results of LC-MS/MS and PRM quantitative analyses, we selected two phosphorylation sites, Thr-225 and Ser-262, which have a higher abundance during senescence, and demonstrated that they play a key role in the function of ERD7 in regulating senescence. Transgenic plants overexpressing the phospho-mimetic mutant of the activation segment residues ERD7T225D and ERD7T262D exhibited a significantly early senescence, while the inactivation segment ERD7T225A and ERD7T262A displayed a delayed senescence. Moreover, we found that ERD7 regulates ROS accumulation by enhancing the expression of AtrbohD and AtrbohF, which is dependent on the critical residues, i.e., Thr-225 and Ser-262. Our findings suggest that ERD7 is a positive regulator of senescence, which might function as a crosstalk hub between age-dependent and stress-induced leaf senescence.

Two adjacent NAC transcription factors regulate fruit maturity date and flavor in peach

Although maturity date (MD) is an essential factor affecting fresh fruit marketing and has a pleiotropic effect on fruit taste qualities, the underlying mechanisms remain largely unclear. In this study, we functionally characterized two adjacent NAM-ATAF1/2-CUC2 (NAC) transcription factors (TFs), PpNAC1 and PpNAC5, both of which were associated with fruit MD in peach. PpNAC1 and PpNAC5 were found capable of activating transcription of genes associated with cell elongation, cell wall degradation and ethylene biosynthesis, suggesting their regulatory roles in fruit enlargement and ripening. Furthermore, PpNAC1 and PpNAC5 had pleiotropic effects on fruit taste due to their ability to activate transcription of genes for sugar accumulation and organic acid degradation. Interestingly, both PpNAC1 and PpNAC5 orthologues were found in fruit-producing angiosperms and adjacently arranged in all 91 tested dicots but absent in fruitless gymnosperms, suggesting their important roles in fruit development. Our results provide insight into the regulatory roles of NAC TFs in MD and fruit taste.

NACs, generalist in plant life

Plant-specific NAC proteins constitute a major transcription factor family that is well-known for its roles in plant growth, development, and responses to abiotic and biotic stresses. In recent years, there has been significant progress in understanding the functions of NAC proteins. NAC proteins have a highly conserved DNA-binding domain; however, their functions are diverse. Previous understanding of the structure of NAC transcription factors can be used as the basis for their functional diversity. NAC transcription factors consist of a target-binding domain at the N-terminus and a highly versatile C-terminal domain that interacts with other proteins. A growing body of research on NAC transcription factors helps us comprehend the intricate signalling network and transcriptional reprogramming facilitated by NAC-mediated complexes. However, most studies of NAC proteins have been limited to a single function. Here, we discuss the upstream regulators, regulatory components and targets of NAC in the context of their prospective roles in plant improvement strategies via biotechnology intervention, highlighting the importance of the NAC transcription factor family in plants and the need for further research.

Functional characterization of two NAC transcription factors HfNAP1 and HfNAC090 associated with flower programmed cell death in daylily (Hemerocallis fulva)

Daylily (Hemerocallis fulva) is one of the most widely used perennial flowers, but its ornamental and economic value is greatly limited due to its ephemeral flowering period. In general, the flower senescence is regulated by the developmental signals and considered as an irreversible process of programmed cell death (PCD). However, the molecular mechanism of flower PCD in daylily still remains unclear. In this study, two NAC transcription factors, namely HfNAP1 and HfNAC090, are first identified and found to be upregulated significantly in both the age-induced and the ABA-induced flower PCD processes in daylily. Then, the functions of HfNAP1 and HfNAC090 in regulating the flower PCD are investigated through transgenic phenotypes analysis. The results demonstrate that the ectopic and transient overexpression of these two genes can effectively regulate the flower PCD in tobacco and daylily. While the overexpression of HfNAP1 accelerates the flower PCD process, the overexpression of HfNAC090 significantly delays that. Furthermore, the yeast two-hybrid assay is performed to discover potential interactions related to these two genes, and the results demonstrate that HfNAP1 and HfNAC090 can interact with each other, or interact with other flower aging-related genes. Additionally, the yeast one-hybrid assay suggests that HfNAP1 and HfNAC090 can bind directly to the promoters of downstream senescence-associated genes HfSAG39 and HfSAG15. Taken overall, this study provides sufficient evidences to confirm that HfNAP1 and HfNAC090 play dominant roles in regulating the flower PCD in daylily, supporting the development of new strategies to prolong the longevity of daylily flowers.

Involvement of CONSTANS-like Proteins in Plant Flowering and Abiotic Stress Response

The process of flowering in plants is a pivotal stage in their life cycle, and the CONSTANS-like (COL) protein family, known for its photoperiod sensing ability, plays a crucial role in regulating plant flowering. Over the past two decades, homologous genes of COL have been identified in various plant species, leading to significant advancements in comprehending their involvement in the flowering pathway and response to abiotic stress. This article presents novel research progress on the structural aspects of COL proteins and their regulatory patterns within transcription complexes. Additionally, we reviewed recent information about their participation in flowering and abiotic stress response, aiming to provide a more comprehensive understanding of the functions of COL proteins.

The ABA-AtNAP-SAG113 PP2C module regulates leaf senescence by dephoshorylating SAG114 SnRK3.25 in Arabidopsis

We previously reported that ABA inhibits stomatal closure through AtNAP-SAG113 PP2C regulatory module during leaf senescence. The mechanism by which this module exerts its function is unknown. Here we report the identification and functional analysis of SAG114, a direct target of the regulatory module. SAG114 encodes SnRK3.25. Both bimolecular fluorescence complementation (BiFC) and yeast two-hybrid assays show that SAG113 PP2C physically interacts with SAG114 SnRK3.25. Biochemically the SAG113 PP2C dephosphorylates SAG114 in vitro and in planta. RT-PCR and GUS reporter analyses show that SAG114 is specifically expressed in senescing leaves in Arabidopsis. Functionally, the SAG114 knockout mutant plants have a significantly bigger stomatal aperture and a much faster water loss rate in senescing leaves than those of wild type, and display a precocious senescence phenotype. The premature senescence phenotype of sag114 is epistatic to sag113 (that exhibits a remarkable delay in leaf senescence) because the sag113 sag114 double mutant plants show an early leaf senescence phenotype, similar to that of sag114. These results not only demonstrate that the ABA-AtNAP-SAG113 PP2C regulatory module controls leaf longevity by dephosphorylating SAG114 kinase, but also reveal the involvement of the SnRK3 family gene in stomatal movement and water loss during leaf senescence.

CHLORIDE CHANNEL-b mediates vacuolar nitrate efflux to improve low nitrogen adaptation in Arabidopsis

The vacuole is an important organelle for nitrate storage, and the reuse of vacuolar nitrate under nitrate starvation helps plants adapt to low-nitrate environments. CHLORIDE CHANNEL-b (CLC-b) in the vacuolar membrane is a nitrate transporter; however, its regulation and effects on nitrate efflux have not been established. Here, we evaluated CLC-b expression and its effects on physiological parameters under low nitrate conditions. CLC-b expression increased significantly in the roots of wild-type Arabidopsis (Arabidopsis thaliana) Col-0 under nitrate starvation. Under low nitrate, clcb mutants showed reductions in chlorophyll content and xylem sap nitrate concentration, shoot/root nitrate ratios, shoot/root total N ratios, and biomass. CLC-b-overexpression yielded opposite phenotypes and increased nitrogen use efficiency. CLC-b mutants showed elevated chlorate tolerance and an increased proportion of vacuolar nitrate relative to the total protoplast nitrate content as compared to the wild type. Yeast 1-hybrid, EMSA, and chromatin immunoprecipitation (ChIP) experiments showed that HRS1 HOMOLOG2 (HHO2), the expression of which is downregulated under low nitrate, binds directly to the promoter of CLC-b. clcb/hho2 double mutants and HHO2-overexpressing clcb plants had similar phenotypes under low nitrate to those of clcb single mutants. Thus, CLC-b mediates vacuolar nitrate efflux and is negatively regulated by HHO2, providing a theoretical basis for improving plant adaptability to low nitrate.

Systemic movement of long non-coding RNA ELENA1 attenuates leaf senescence under nitrogen deficiency

Nitrogen is an essential macronutrient that is absorbed by roots and stored in leaves, mainly as ribulose-1,5-bisphosphate carboxylase/oxygenase1,2. During nitrogen deficiency (-N), plants activate leaf senescence for source-to-sink nitrogen remobilization for adaptative growth3-6. However, how -N signals perceived by roots are propagated to shoots remains underexplored. We found that ELF18-INDUCED LONG NONCODING RNA 1 (ELENA1) is -N inducible and attenuates -N-induced leaf senescence in Arabidopsis. Analysis of plants expressing the ELENA1 promoter β-glucuronidase fusion gene showed that ELENA1 is transcribed specifically in roots under -N. Reciprocal grafting of the wild type and elena1 demonstrated that ELENA1 functions systemically. ELENA1 dissociates the MEDIATOR SUBUNIT 19a-ORESARA1 transcriptional complex, thereby calibrating senescence progression. Our observations establish the systemic regulation of leaf senescence by a root-derived long non-coding RNA under -N in Arabidopsis.

NAC domain transcription factors VNI2 and ATAF2 form protein complexes and regulate leaf senescence

The NAM, ATAF1/2, and CUC2 (NAC) domain transcription factor VND-INTERACTING2 (VNI2) negatively regulates xylem vessel formation by interacting with another NAC domain transcription factor, VASCULAR-RELATED NAC-DOMAIN7 (VND7), a master regulator of xylem vessel formation. Here, we screened interacting proteins with VNI2 using yeast two-hybrid assay and isolated two NAC domain transcription factors, Arabidopsis thaliana ACTIVATION FACTOR 2 (ATAF2) and NAC DOMAIN CONTAINING PROTEIN 102 (ANAC102). A transient gene expression assay showed that ATAF2 upregulates the expression of genes involved in leaf senescence, and VNI2 effectively inhibits the transcriptional activation activity of ATAF2. vni2 mutants accelerate leaf senescence, whereas ataf2 mutants delay leaf senescence. In addition, the accelerated leaf senescence phenotype of the vni2 mutant is recovered by simultaneous mutation of ATAF2. Our findings strongly suggest that VNI2 interacts with and inhibits ATAF2, resulting in negatively regulating leaf senescence.

GmNAC039 and GmNAC018 activate the expression of cysteine protease genes to promote soybean nodule senescence

Root nodules are major sources of nitrogen for soybean (Glycine max (L.) Merr.) growth, development, production, and seed quality. Symbiotic nitrogen fixation is time-limited, as the root nodule senesces during the reproductive stage of plant development, specifically during seed development. Nodule senescence is characterized by the induction of senescence-related genes, such as papain-like cysteine proteases (CYPs), which ultimately leads to the degradation of both bacteroids and plant cells. However, how nodule senescence-related genes are activated in soybean is unknown. Here, we identified 2 paralogous NAC transcription factors, GmNAC039 and GmNAC018, as master regulators of nodule senescence. Overexpression of either gene induced soybean nodule senescence with increased cell death as detected using a TUNEL assay, whereas their knockout delayed senescence and increased nitrogenase activity. Transcriptome analysis and nCUT&Tag-qPCR assays revealed that GmNAC039 directly binds to the core motif CAC(A)A and activates the expression of 4 GmCYP genes (GmCYP35, GmCYP37, GmCYP39, and GmCYP45). Similar to GmNAC039 and GmNAC018, overexpression or knockout of GmCYP genes in nodules resulted in precocious or delayed senescence, respectively. These data provide essential insights into the regulatory mechanisms of nodule senescence, in which GmNAC039 and GmNAC018 directly activate the expression of GmCYP genes to promote nodule senescence.

Abiotic Stress-Induced Leaf Senescence: Regulatory Mechanisms and Application

Leaf senescence is a natural phenomenon that occurs during the aging process of plants and is influenced by various internal and external factors. These factors encompass plant hormones, as well as environmental pressures such as inadequate nutrients, drought, darkness, high salinity, and extreme temperatures. Abiotic stresses accelerate leaf senescence, resulting in reduced photosynthetic efficiency, yield, and quality. Gaining a comprehensive understanding of the molecular mechanisms underlying leaf senescence in response to abiotic stresses is imperative to enhance the resilience and productivity of crops in unfavorable environments. In recent years, substantial advancements have been made in the study of leaf senescence, particularly regarding the identification of pivotal genes and transcription factors involved in this process. Nevertheless, challenges remain, including the necessity for further exploration of the intricate regulatory network governing leaf senescence and the development of effective strategies for manipulating genes in crops. This manuscript provides an overview of the molecular mechanisms that trigger leaf senescence under abiotic stresses, along with strategies to enhance stress tolerance and improve crop yield and quality by delaying leaf senescence. Furthermore, this review also highlighted the challenges associated with leaf senescence research and proposes potential solutions.

Transcriptome-Wide Identification and Response Pattern Analysis of the Salix integra NAC Transcription Factor in Response to Pb Stress

The NAC (NAM-ATAF1/2-CUC) transcription factor family is one of the largest plant-specific transcription factor families, playing an important role in plant growth and development and abiotic stress response. As a short-rotation woody plant, Salix integra (S. integra) has high lead (Pb) phytoremediation potential. To understand the role of NAC in S. integra Pb tolerance, 53 SiNAC transcripts were identified using third-generation and next-generation transcriptomic data from S. integra exposed to Pb stress, and a phylogenetic analysis revealed 11 subfamilies. A sequence alignment showed that multiple subfamilies represented by TIP and ATAF had a gene that produced more than one transcript under Pb stress, and different transcripts had different responses to Pb. By analyzing the expression profiles of SiNACs at 9 Pb stress time points, 41 of 53 SiNACs were found to be significantly responsive to Pb. Short time-series expression miner (STEM) analysis revealed that 41 SiNACs had two significant Pb positive response patterns (early and late), both containing 10 SiNACs. The SiNACs with the most significant Pb response were mainly from the ATAF and NAP subfamilies. Therefore, 4 and 3 SiNACs from the ATAF and NAP subfamilies, respectively, were selected as candidate Pb-responsive SiNACs for further structural and functional analysis. The RT-qPCR results of 7 transcripts also confirmed the different Pb response patterns of the ATAF and NAP subfamilies. SiNAC004 and SiNAC120, which were randomly selected from two subfamilies, were confirmed to be nuclear localization proteins by subcellular localization experiments. Functional prediction analysis of the associated transcripts of seven candidate SiNACs showed that the target pathways of ATAF subfamily SiNACs were "sulfur metabolism" and "glutathione metabolism", and the target pathways of NAP subfamily SiNACs were "ribosome" and "phenylpropanoid biosynthesis". This study not only identified two NAC subfamilies with different Pb response patterns but also identified Pb-responsive SiNACs that could provide a basis for subsequent gene function verification.

Receptor for Activated C Kinase1B (RACK1B) Delays Salinity-Induced Senescence in Rice Leaves by Regulating Chlorophyll Degradation

The widely conserved Receptor for Activated C Kinase1 (RACK1) protein is a WD-40 type scaffold protein that regulates diverse environmental stress signal transduction pathways. Arabidopsis RACK1A has been reported to interact with various proteins in salt stress and Light-Harvesting Complex (LHC) pathways. However, the mechanism of how RACK1 contributes to the photosystem and chlorophyll metabolism in stress conditions remains elusive. In this study, using T-DNA-mediated activation tagging transgenic rice (Oryza sativa L.) lines, we show that leaves from rice RACK1B gene (OsRACK1B) gain-of-function (RACK1B-OX) plants exhibit the stay-green phenotype under salinity stress. In contrast, leaves from down-regulated OsRACK1B (RACK1B-UX) plants display an accelerated yellowing. qRT-PCR analysis revealed that several genes which encode chlorophyll catabolic enzymes (CCEs) are differentially expressed in both RACK1B-OX and RACK1B-UX rice plants. In addition to CCEs, stay-green (SGR) is a key component that forms the SGR-CCE complex in senescing chloroplasts, and which causes LHCII complex instability. Transcript and protein profiling revealed a significant upregulation of OsSGR in RACK1B-UX plants compared to that in RACK1B-OX rice plants during salt treatment. The results imply that senescence-associated transcription factors (TFs) are altered following altered OsRACK1B expression, indicating a transcriptional reprogramming by OsRACK1B and a novel regulatory mechanism involving the OsRACK1B-OsSGR-TFs complex. Our findings suggest that the ectopic expression of OsRACK1B negatively regulates chlorophyll degradation, leads to a steady level of LHC-II isoform Lhcb1, an essential prerequisite for the state transition of photosynthesis for adaptation, and delays salinity-induced senescence. Taken together, these results provide important insights into the molecular mechanisms of salinity-induced senescence, which can be useful in circumventing the effect of salt on photosynthesis and in reducing the yield penalty of important cereal crops, such as rice, in global climate change conditions.

Genome-Wide Identification of GATA Family Genes in Phoebe bournei and Their Transcriptional Analysis under Abiotic Stresses

GATA transcription factors are crucial proteins in regulating transcription and are characterized by a type-IV zinc finger DNA-binding domain. They play a significant role in the growth and development of plants. While the GATA family gene has been identified in several plant species, it has not yet been reported in Phoebe bournei. In this study, 22 GATA family genes were identified from the P. bournei genome, and their physicochemical properties, chromosomal distribution, subcellular localization, phylogenetic tree, conserved motif, gene structure, cis-regulatory elements in promoters, and expression in plant tissues were analyzed. Phylogenetic analysis showed that the PbGATAs were clearly divided into four subfamilies. They are unequally distributed across 11 out of 12 chromosomes, except chromosome 9. Promoter cis-elements are mostly involved in environmental stress and hormonal regulation. Further studies showed that PbGATA11 was localized to chloroplasts and expressed in five tissues, including the root bark, root xylem, stem bark, stem xylem, and leaf, which means that PbGATA11 may have a potential role in the regulation of chlorophyll synthesis. Finally, the expression profiles of four representative genes, PbGATA5, PbGATA12, PbGATA16, and PbGATA22, under drought, salinity, and temperature stress, were detected by qRT-PCR. The results showed that PbGATA5, PbGATA22, and PbGATA16 were significantly expressed under drought stress. PbGATA12 and PbGATA22 were significantly expressed after 8 h of low-temperature stress at 10 °C. This study concludes that the growth and development of the PbGATA family gene in P. bournei in coping with adversity stress are crucial. This study provides new ideas for studying the evolution of GATAs, provides useful information for future functional analysis of PbGATA genes, and helps better understand the abiotic stress response of P. bournei.

The NAC transcription factor ZmNAC132 regulates leaf senescence and male fertility in maize

Leaf senescence is an integral step in the final stages of plant development, as nutrient remobilization from leaves to sink organs is accomplished during this process. NACs compose a large superfamily of plant-specific TFs involved in multiple plant development processes. Here, we identified a maize NAC TF, ZmNAC132, involved in leaf senescence and male fertility. ZmNAC132 expression was tightly linked to leaf senescence in an age-dependent manner. Knockout of ZmNAC132 led to delays in chlorophyll degradation and leaf senescence, whereas overexpression of ZmNAC132 had the opposite effects. ZmNAC132 could bind to and transactivate the promoter of ZmNYE1, a major chlorophyll catabolic gene, to accelerate chlorophyll degradation during leaf senescence. Moreover, ZmNAC132 affected male fertility through the upregulation of ZmEXPB1, an expansin-encoding gene associated with sexual reproduction and other related genes. Together, the results show that ZmNAC132 participates in the regulation of leaf senescence and male fertility through the targeting of different downstream genes in maize.

Chromatin accessibility dynamics insight into crosstalk between regulatory landscapes in poplar responses to multiple treatments

Perennial trees develop and coordinate endogenous response signaling pathways, including their crosstalk and convergence, to cope with various environmental stresses which occur simultaneously in most cases. These processes are involved in gene transcriptional regulations that depend on dynamic interactions between regulatory proteins and corresponding chromatin regions, but the mechanisms remain poorly understood in trees. In this study, we detected chromatin regulatory landscapes of poplar under abscisic acid, methyl jasmonate, salicylic acid and sodium chloride (NaCl) treatment, through integrating ATAC-seq and RNA-seq data. Our results showed that the degree of chromatin accessibility for a given gene is closely related to its expression level. However, unlike the gene expression that shows treatment-specific response patterns, changes in chromatin accessibility exhibit high similarities under these treatments. We further proposed and experimentally validated that a homologous gene copy of RESPONSIVE TO DESICCATION 26 mediates the crosstalk between jasmonic acid and NaCl signaling pathways by directly regulating the stress-responsive genes and that circadian clock-related transcription factors like REVEILLE8 play a central role in response of poplar to these treatments. Overall, our study provides a chromatin insight into the molecular mechanism of transcription regulatory networks in response to different environmental stresses and raises the key roles of the circadian clock of poplar to adapt to adverse environments.

Transcription Factors-Regulated Leaf Senescence: Current Knowledge, Challenges and Approaches

Leaf senescence is a complex biological process regulated at multiple levels, including chromatin remodeling, transcription, post-transcription, translation, and post-translational modifications. Transcription factors (TFs) are crucial regulators of leaf senescence, with NAC and WRKY families being the most studied. This review summarizes the progress made in understanding the regulatory roles of these families in leaf senescence in Arabidopsis and various crops such as wheat, maize, sorghum, and rice. Additionally, we review the regulatory functions of other families, such as ERF, bHLH, bZIP, and MYB. Unraveling the mechanisms of leaf senescence regulated by TFs has the potential to improve crop yield and quality through molecular breeding. While significant progress has been made in leaf senescence research in recent years, our understanding of the molecular regulatory mechanisms underlying this process is still incomplete. This review also discusses the challenges and opportunities in leaf senescence research, with suggestions for possible strategies to address them.

Structural basis of DNA binding by the NAC transcription factor ORE1, a master regulator of plant senescence

Plants use sophisticated mechanisms of gene expression to control senescence in response to environmental stress or aging. ORE1 (Arabidopsis thaliana NAC092) is a master regulator of senescence that belongs to the plant-specific NAC transcription factor protein family. ORE1 has been reported to bind to multiple DNA targets to orchestrate leaf senescence, yet the mechanistic basis for recognition of the cognate gene sequence remains unclear. Here, we report the crystal structure of the ORE1-NAC domain alone and its DNA-binding form. The structure of DNA-bound ORE1-NAC revealed the molecular basis for nucleobase recognition and phosphate backbone interactions. We show that local versatility in the DNA-binding site, in combination with domain flexibility of the ORE-NAC homodimer, is crucial for the maintenance of binding to intrinsically flexible DNA. Our results provide a platform for understanding other plant-specific NAC protein-DNA interactions as well as insight into the structural basis of NAC regulators in plants of agronomic and scientific importance.

Increasingly amplified stimulation mediated by TaNAC69-B is crucial for the leaf senescence in wheat

Leaf senescence involves massive multidimensional alterations, such as nutrient redistribution, and is closely related to crop yield and quality. No apical meristem, Arabidopsis transcription activation factor, and Cup-shaped cotyledon (NAC)-type transcription factors integrate various signals and modulate an enormous number of target genes to ensure the appropriate progression of leaf senescence. However, few leaf senescence-related NACs have been functionally characterized in wheat. Based on our previous RNA-sequencing (RNA-seq) data, we focused on a NAC family member, TaNAC69-B, which is increasingly expressed during leaf senescence in wheat. Overexpression of TaNAC69-B led to precocious leaf senescence in wheat and Arabidopsis, and affected several agricultural traits in transgenic wheat. Moreover, impaired expression of TaNAC69-B by virus-induced gene silencing retarded the leaf senescence in wheat. By RNA-seq and quantitative real-time polymerase chain reaction analysis, we confirmed that some abscisic acid (ABA) biosynthesis genes, including AAO3 and its ortholog in wheat, TraesCS2B02G270600 (TaAO3-B), were elevated by the overexpression of TaNAC69-B. Consistently, we observed more severe ABA-induced leaf senescence in TaNAC69-B-OE wheat and Arabidopsis plants. Furthermore, we determined that TaNAC69-B bound to the NAC binding site core (CGT) on the promoter regions of AAO3 and TaAO3-B. Moreover, we confirmed elevated ABA levels in TaNAC69-B-OE wheat lines. Although TaNAC69-B shares 39.83% identity (amino acid) with AtNAP, TaNAC69-B did not completely restore the delayed leaf senescence in the atnap mutant. Collectively, our results revealed a positive feedback loop, consisting of TaNAC69-B, ABA biosynthesis and leaf senescence, that is essential for the regulation of leaf senescence in wheat.

Catalase: A critical node in the regulation of cell fate

Catalase (CAT) is an extensively studied if somewhat enigmatic enzyme that is at the heart of eukaryotic antioxidant systems with a canonical role in peroxisomal function. The CAT family of proteins exert control over a wide range of plant growth and defence processes. CAT proteins are subject to many types of post-translational modification (PTM), which modify activity, ligand binding, stability, compartmentation and function. The CAT interactome involves many cytosolic and nuclear proteins that appear to be essential for protein functions. Hence, the CAT network of roles extends far beyond those associated with peroxisomal metabolism. Some pathogen effector proteins are able to redirect CAT to the nucleus and recent evidence indicates CAT can traffic to the nucleus in the absence of exogenous proteins. While the mechanisms that target CAT to the nucleus are not understood, CAT activity in the cytosol and nucleus is promoted by interactions with nucleoredoxin. Here we discuss recent findings that have been pivotal in generating a step change in our understanding of CAT functions in plant cells.

Enrichment of intrinsically disordered residues in ohnologs facilitates abiotic stress resilience in Brassica rapa

Arabidopsis thaliana and Brassica rapa are in the same evolutionary lineage, although the latter experienced an additional whole genome triplication event. Therefore, it would be intriguing to investigate the traits that gene duplication imposes to mediate plant stress tolerance. Here, we noticed that B. rapa abiotic stress resistance (ASR) genes which code at least one stress responsive domain have a significantly higher number of paralogs than A. thaliana. Analysing the disordered content of the ASR genes in both species, we found that intrinsically disordered residues (IDR) are specifically enriched in whole genome duplication (WGD) derived paralogs. Subsequently, domain similarity analysis between WGD pairs of both species has revealed that majority of WGD pairs in B. rapa did not share domains with each other. Furthermore, domain enrichment analysis has shown that B. rapa paralogs contain 36 distinct stress responsive enriched domains, significantly higher than A. thaliana paralogs. Next, we performed MSA to investigate the domain conservation between orthologs and ohnologs pairs, we found that 80.13% of B. rapa ohnologs acquire new domains, depicting the fact that ohnologs play a significant role in stress-related behaviours. The average IDR content of the ohnologs enriching new domains after gene duplication in B. rapa (0.19), is also significantly higher than A. thaliana (0.04). Interestingly, we also found that all of these attributes i.e., exhibiting higher number of WGD paralogs and enhancement of IDR in ASR genes of B. rapa compared to A. thaliana is exclusive for ASR genes only. No such significant differences were observed in randomly selected non-ASR genes between the two species. Together these results provide strong support for the hypothesis that augmentation of IDR content followed by a whole genome duplication event imposes the stress resistance potentiality in B. rapa. This research will shed light on the mechanism of how B. rapa is able to successfully adapt to stress over the evolutionary timescale.

Genome-wide identification, evolution and expression analysis of NAC gene family under salt stress in wild emmer wheat (Triticum dicoccoides. L)

The NAC transcription factor (TF) family is one of the largest plant-specific gene families, playing the vital roles in plant growth and development as well as stress response. Although it has been extensively characterized in many plants, the significance of NAC family in wild emmer wheat is not well understood up to now. Here, a total of 200 NAC transcription factors were identified in wild emmer (TdNACs) through a genome-search method, which were classified into 12 subfamilies based on phylogenetic relationship. And the members in the subfamily shared similar exon-intron structure and conversed domain organization. Collinearity analysis revealed that segmental duplication and polyploidization contributed mainly to the expansion of TdNACs. Furthermore, the genetic variations of TdNACs were investigated using the re-sequencing data and genetic bottleneck has occurred on NAC genes when wild emmer domesticated to cultivated emmer wheat. Finally, the expression patterns of these TdNACs were investigated using RNA-seq data of the salt-tolerant genotype under salt stress to obtain salt-responsive TdNACs, and 10 out of which were further validated using QPCR analysis. This study provided the targets for further functional study of TdNAC genes, and also contributed to mine novel genes for improving the salt tolerance in wheat and other crops.

Transcriptome-wide identification of NAC (no apical meristem/Arabidopsis transcription activation factor/cup-shaped cotyledon) transcription factors potentially involved in salt stress response in garlic

Soil salinity has been an increasing problem worldwide endangering crop production and human food security. It is an ideal strategy to excavate stress resistant genes and develop salt tolerant crops. NAC (no apical meristem/Arabidopsis transcription activation factor/cup-shaped cotyledon) transcription factors have been demonstrated to be involved in salt stress response. However, relevant studies have not been observed in garlic, an important vegetable consumed in the world. In this study, a total of 46 AsNAC genes encoding NAC proteins were identified in garlic plant by transcriptome data. Phylogenetic analysis showed that the examined AsNAC proteins were clustered into 14 subgroups. Motif discovery revealed that the conserved domain region was mainly composed of five conserved subdomains. Most of the genes selected could be induced by salt stress in different tissues, indicating a potential role in salt stress response. Further studies may focus on the molecular mechanisms of the AsNAC genes in salt stress response. The results of the current work provided valuable resources for researchers aimed at developing salt tolerant crops.

The IbPYL8-IbbHLH66-IbbHLH118 complex mediates the abscisic acid-dependent drought response in sweet potato

Drought limits crop development and yields. bHLH (basic helix-loop-helix) transcription factors play critical roles in regulating the drought response in many plants, but their roles in this process in sweet potato are unknown. Here, we report that two bHLH proteins, IbbHLH118 and IbbHLH66, play opposite roles in the ABA-mediated drought response in sweet potato. ABA treatment repressed IbbHLH118 expression but induced IbbHLH66 expression in the drought-tolerant sweet potato line Xushu55-2. Overexpressing IbbHLH118 reduced drought tolerance, whereas overexpressing IbbHLH66 enhanced drought tolerance, in sweet potato. IbbHLH118 directly binds to the E-boxes in the promoters of ABA-insensitive 5 (IbABI5), ABA-responsive element binding factor 2 (IbABF2) and tonoplast intrinsic protein 1 (IbTIP1) to suppress their transcription. IbbHLH118 forms homodimers with itself or heterodimers with IbbHLH66. Both of the IbbHLHs interact with the ABA receptor IbPYL8. ABA accumulates under drought stress, promoting the formation of the IbPYL8-IbbHLH66-IbbHLH118 complex. This complex interferes with IbbHLH118's repression of ABA-responsive genes, thereby activating ABA responses and enhancing drought tolerance. These findings shed light on the role of the IbPYL8-IbbHLH66-IbbHLH118 complex in the ABA-dependent drought response of sweet potato and identify candidate genes for developing elite crop varieties with enhanced drought tolerance.

Protein Kinase RhCIPK6 Promotes Petal Senescence in Response to Ethylene in Rose (Rosa Hybrida)

Cultivated roses have the largest global market share among ornamental crops. Postharvest release of ethylene is the main cause of accelerated senescence and decline in rose flower quality. To understand the molecular mechanism of ethylene-induced rose petal senescence, we analyzed the transcriptome of rose petals during natural senescence as well as with ethylene treatment. A large number of differentially expressed genes (DEGs) were observed between developmental senescence and the ethylene-induced process. We identified 1207 upregulated genes in the ethylene-induced senescence process, including 82 transcription factors and 48 protein kinases. Gene Ontology enrichment analysis showed that ethylene-induced senescence was closely related to stress, dehydration, and redox reactions. We identified a calcineurin B-like protein (CBL) interacting protein kinase (CIPK) family gene in Rosa hybrida, RhCIPK6, that was regulated by age and ethylene induction. Reducing RhCIPK6 expression through virus-induced gene silencing significantly delayed petal senescence, indicating that RhCIPK6 mediates petal senescence. In the RhCIPK6-silenced petals, several senescence associated genes (SAGs) and transcription factor genes were downregulated compared with controls. We also determined that RhCIPK6 directly binds calcineurin B-like protein 3 (RhCBL3). Our work thus offers new insights into the function of CIPKs in petal senescence and provides a genetic resource for extending rose vase life.

NAC transcription factor TgNAP promotes tulip petal senescence

Petal senescence is a crucial determinant for ornamental quality and economic value of floral crops. Salicylic acid (SA) and reactive oxygen species (ROS) are two prominent factors involved in plant senescence regulation. In this study, tulip TgNAP (NAC-like, activated by APETALA3/PISTILLATA) was characterized as positively regulating tulip petal senescence through dually regulating SA biosynthesis and ROS detoxification pathways. TgNAP was upregulated in senescing petals of tulip while exogenous SA and H2O2 treatments substantially promoted petal senescence in tulip. Silencing of TgNAP by VIGS assay delayed SA and H2O2-induced petal senescence in tulip, whereas overexpression of TgNAP promoted the senescence process in Arabidopsis (Arabidopsis thaliana) plants. Additionally, inhibition of SA biosynthesis prolonged the lifespan of TgNAP-silenced petal discs. Further evidence indicated that TgNAP activates the transcriptions of two key SA biosynthetic genes ISOCHORISMATE SYNTHASE 1 (TgICS1) and PHENYLALANINE AMMONIA-LYASE 1 (TgPAL1) through directly binding to their promoter regions. Meanwhile, TgNAP repressed ROS scavenging by directly inhibiting PEROXIDASE 12 (POD12) and POD17 expression. Taken together, these results indicate that TgNAP enhances SA biosynthesis and ROS accumulation to positively regulate petal senescence in tulip.

Characterization of NAC transcription factor NtNAC028 as a regulator of leaf senescence and stress responses

NAC proteins constitute one of the largest transcription factor families and are involved in regulation of plant development and stress responses. Our previous transcriptome analyses of tobacco revealed a significant increase in the expression of NtNAC028 during leaf yellowing. In this study, we found that NtNAC028 was rapidly upregulated in response to high salinity, dehydration, and abscisic acid (ABA) stresses, suggesting a vital role of this gene in abiotic stress response. NtNAC028 loss-of-function tobacco plants generated via CRISPR-Cas9 showed delayed leaf senescence and increased tolerance to drought and salt stresses. Meanwhile NtNAC028 overexpression led to precocious leaf senescence and hypersensitivity to abiotic stresses in Arabidopsis, indicating that NtNAC028 functions as a positive regulator of natural leaf senescence and a negative regulator of stress tolerance. Furthermore, NtNAC028-overexpressing Arabidopsis plants showed lower antioxidant enzyme activities, higher reactive oxygen species (ROS), and H2O2 accumulation under high salinity, resulted in more severe oxidative damage after salt stress treatments. On the other hand, NtNAC028 mutation in tobacco resulted in upregulated expression of ROS-scavenging and abiotic stress-related genes, higher antioxidant enzyme activities, and enhanced tolerance against abiotic stresses, suggesting that NtNAC028 might act as a vital regulator for plant stress response likely by mediating ROS scavenging ability. Collectively, our results indicated that the NtNAC028 plays a key regulatory role in leaf senescence and response to multiple abiotic stresses.

Know when and how to die: gaining insights into the molecular regulation of leaf senescence

Senescence is the ultimate phase in the life cycle of leaves which is crucial for recycling of nutrients to maintain plant fitness and reproductive success. The earliest visible manifestation of leaf senescence is their yellowing, which usually commences with the breakdown of chlorophyll. The degradation process involves a gradual and highly coordinated disassembly of macromolecules resulting in the accumulation of nutrients, which are subsequently mobilized from the senescing leaves to the developing organs. Leaf senescence progresses under overly tight genetic and molecular control involving a well-orchestrated and intricate network of regulators that coordinate spatio-temporally with the influence of both internal and external cues. Owing to the advancements in omics technologies, the availability of mutant resources, scalability of molecular analyses methodologies and the advanced capacity to integrate multidimensional data, our understanding of the genetic and molecular basis of leaf ageing has greatly expanded. The review provides a compilation of the multitier regulation of senescence process and the interrelation between the environment and the terminal phase of leaf development. The knowledge gained would benefit in devising the strategies for manipulation of leaf senescence process to improve crop quality and productivity.

Metabolic control of arginine and ornithine levels paces the progression of leaf senescence

Leaf senescence can be induced by stress or aging, sometimes in a synergistic manner. It is generally acknowledged that the ability to withstand senescence-inducing conditions can provide plants with stress resilience. Although the signaling and transcriptional networks responsible for a delayed senescence phenotype, often referred to as a functional stay-green trait, have been actively investigated, very little is known about the subsequent metabolic adjustments conferring this aptitude to survival. First, using the individually darkened leaf (IDL) experimental setup, we compared IDLs of wild-type (WT) Arabidopsis (Arabidopsis thaliana) to several stay-green contexts, that is IDLs of two functional stay-green mutant lines, oresara1-2 (ore1-2) and an allele of phytochrome-interacting factor 5 (pif5), as well as to leaves from a WT plant entirely darkened (DP). We provide compelling evidence that arginine and ornithine, which accumulate in all stay-green contexts-likely due to the lack of induction of amino acids (AAs) transport-can delay the progression of senescence by fueling the Krebs cycle or the production of polyamines (PAs). Secondly, we show that the conversion of putrescine to spermidine (SPD) is controlled in an age-dependent manner. Thirdly, we demonstrate that SPD represses senescence via interference with ethylene signaling by stabilizing the ETHYLENE BINDING FACTOR1 and 2 (EBF1/2) complex. Taken together, our results identify arginine and ornithine as central metabolites influencing the stress- and age-dependent progression of leaf senescence. We propose that the regulatory loop between the pace of the AA export and the progression of leaf senescence provides the plant with a mechanism to fine-tune the induction of cell death in leaves, which, if triggered unnecessarily, can impede nutrient remobilization and thus plant growth and survival.

To have or not to have: expression of amino acid transporters during pathogen infection

The interaction between plants and plant pathogens can have significant effects on ecosystem performance. For their growth and development, both bionts rely on amino acids. While amino acids are key transport forms of nitrogen and can be directly absorbed from the soil through specific root amino acid transporters, various pathogenic microbes can invade plant tissues to feed on different plant amino acid pools. In parallel, plants may initiate an immune response program to restrict this invasion, employing various amino acid transporters to modify the amino acid pool at the site of pathogen attack. The interaction between pathogens and plants is sophisticated and responses are dynamic. Both avail themselves of multiple tools to increase their chance of survival. In this review, we highlight the role of amino acid transporters during pathogen infection. Having control over the expression of those transporters can be decisive for the fate of both bionts but the underlying mechanism that regulates the expression of amino acid transporters is not understood to date. We provide an overview of the regulation of a variety of amino acid transporters, depending on interaction with biotrophic, hemibiotrophic or necrotrophic pathogens. In addition, we aim to highlight the interplay of different physiological processes on amino acid transporter regulation during pathogen attack and chose the LYSINE HISTIDINE TRANSPORTER1 (LHT1) as an example.

Ethylene responsive factor34 mediates stress-induced leaf senescence by regulating salt stress-responsive genes

Leaf senescence proceeds with age but is modulated by various environmental stresses and hormones. Salt stress is one of the most well-known environmental stresses that accelerate leaf senescence. However, the molecular mechanisms that integrate salt stress signalling with leaf senescence programmes remain elusive. In this study, we characterised the role of ETHYLENE RESPONSIVE FACTOR34 (ERF34), an Arabidopsis APETALA2 (AP2)/ERF family transcription factor, in leaf senescence. ERF34 was differentially expressed under various leaf senescence-inducing conditions, and negatively regulated leaf senescence induced by age, dark, and salt stress. ERF34 also promoted salt stress tolerance at different stages of the plant life cycle such as seed germination and vegetative growth. Transcriptome analysis revealed that the overexpression of ERF34 increased the transcript levels of salt stress-responsive genes including COLD-REGULATED15A (COR15A), EARLY RESPONSIVE TO DEHYDRATION10 (ERD10), and RESPONSIVE TO DESICCATION29A (RD29A). Moreover, ERF34 directly bound to ERD10 and RD29A promoters and activated their expression. Our findings indicate that ERF34 plays a key role in the convergence of the salt stress response with the leaf senescence programmes, and is a potential candidate for crop improvement, particularly by enhancing salt stress tolerance.

Maize ZmBES1/BZR1-3 and -9 Transcription Factors Negatively Regulate Drought Tolerance in Transgenic Arabidopsis

The BRI1-EMS suppressor 1 (BES1)/brassinazole-resistant 1(BZR1) transcription factors play crucial roles in plant growth, development, and stress response. However, little is known about the function of maize’s BES1/BZR1s. In this study, the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes were cloned from maize’s inbred line, B73, and they were functionally evaluated by analyzing their expression pattern, subcellular localization, transcriptional activation activity, as well as their heterologous expression in Arabidopsis, respectively. The results of the qRT-PCR showed that the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes were predominantly expressed in the root, and their expression was significantly down-regulated by drought stress. The ZmBES1/BZR1-3 and ZmBES1/BZR1-9 proteins localized in the nucleus but showed no transcriptional activation activity as a monomer. Subsequently, it was found that the heterologous expression of the ZmBES1/BZR1-3 and ZmBES1/BZR1-9 genes in Arabidopsis decreased drought tolerance, respectively. The transgenic lines showed a more serious wilting phenotype, shorter root length, lower fresh weight, and higher relative electrolyte leakage (REL) and malondialdehyde (MDA) content compared to the control under drought stress. The RNA-sequencing data showed that the 70.67% and 93.27% differentially expressed genes (DEGs) were significantly down-regulated in ZmBES1/BZR1-3 and ZmBES1/BZR1-9 transgenic Arabidopsis, respectively. The DEGs of ZmBES1/BZR1-3 gene’s expressing lines were mainly associated with oxidative stress response and amino acid metabolic process and enriched in phenylpropanoid biosynthesis and protein processing in the endoplasmic reticulum. But the DEGs of the ZmBES1/BZR1-9 gene’s expressing lines were predominantly annotated with water deprivation, extracellular stimuli, and jasmonic acid and enriched in phenylpropanoid biosynthesis and plant hormone signal transduction. Moreover, ZmBES1/BZR1-9 increased stomatal aperture in transgenic Arabidopsis under drought stress. This study indicates that ZmBES1/BZR1-3 and ZmBES1/BZR1-9 negatively regulate drought tolerance via different pathways in transgenic Arabidopsis, and it provides insights into the underlying the function of BES1/BZR1s in crops.

Morphological Characterization and Integrated Transcriptome and Proteome Analysis of Organ Development Defective 1 (odd1) Mutant in Cucumis sativus L

Cucumber (Cucumis sativus L.) is an economically important vegetable crop with the unique growth habit and typical trailing shoot architecture of Cucurbitaceae. Elucidating the regulatory mechanisms of growth and development is significant for improving quality and productivity in cucumber. Here we isolated a spontaneous cucumber mutant organ development defective 1 (odd1) with multiple morphological changes including root, plant stature, stem, leaf, male and female flowers, as well as fruit. Anatomical and cytological analyses demonstrated that both cell size and number decreased, and the shoot apical meristem (SAM) was smaller in odd1 compared with WT. Pollen vigor and germination assays and cross tests revealed that odd1 is female sterile, which may be caused by the absence of ovules. Genetic analysis showed that odd1 is a recessive single gene mutant. Using the MutMap strategy, the odd1 gene was found to be located on chromosome 5. Integrated profiling of transcriptome and proteome indicated that the different expression genes related to hormones and SAM maintenance might be the reason for the phenotypic changes of odd1. These results expanded the insight into the molecular regulation of organ growth and development and provided a comprehensive reference map for further studies in cucumber.

Transcriptional Programs and Regulators Underlying Age-Dependent and Dark-Induced Senescence in Medicago truncatula

In forage crops, age-dependent and stress-induced senescence reduces forage yield and quality. Therefore, delaying leaf senescence may be a way to improve forage yield and quality as well as plant resilience to stresses. Here, we used RNA-sequencing to determine the molecular bases of age-dependent and dark-induced leaf senescence in Medicago truncatula. We identified 6845 differentially expressed genes (DEGs) in M3 leaves associated with age-dependent leaf senescence. An even larger number (14219) of DEGs were associated with dark-induced senescence. Upregulated genes identified during age-dependent and dark-induced senescence were over-represented in oxidation–reduction processes and amino acid, carboxylic acid and chlorophyll catabolic processes. Dark-specific upregulated genes also over-represented autophagy, senescence and cell death. Mitochondrial functions were strongly inhibited by dark-treatment while these remained active during age-dependent senescence. Additionally, 391 DE transcription factors (TFs) belonging to various TF families were identified, including a core set of 74 TFs during age-dependent senescence while 759 DE TFs including a core set of 338 TFs were identified during dark-induced senescence. The heterologous expression of several senescence-induced TFs belonging to NAC, WKRY, bZIP, MYB and HD-zip TF families promoted senescence in tobacco leaves. This study revealed the dynamics of transcriptomic responses to age- and dark-induced senescence in M. truncatula and identified senescence-associated TFs that are attractive targets for future work to control senescence in forage legumes.

Phosphorylation of MdERF17 by MdMPK4 promotes apple fruit peel degreening during light/dark transitions

As apple fruits (Malus domestica) mature, they accumulate anthocyanins concomitantly with losing chlorophyll (Chl); however, the molecular pathways and events that coordinate Chl degradation and fruit coloration have not been elucidated. We showed previously that the transcription factor ETHYLENE RESPONSE FACTOR17 (MdERF17) modulates Chl degradation in apple fruit peels and that variation in the pattern of MdERF17 serine (Ser) residues is responsible for differences in its transcriptional regulatory activity. Here, we report that MdERF17 interacts with and is phosphorylated by MAP KINASE4 (MdMPK4-14G). Phosphorylation of MdERF17 at residue Thr67 by MdMPK4-14G is necessary for its transcriptional regulatory activity and its regulation of Chl degradation. We also show that MdERF17 mutants with different numbers of Ser repeat insertions exhibit altered phosphorylation profiles, with more repeats increasing its interaction with MdMPK4. MdMPK4-14G can be activated by exposure to darkness and is involved in the dark-induced degreening of fruit peels. We also demonstrate that greater phosphorylation of MdERF17 by MdMPK4-14G is responsible for the regulation of Chl degradation during light/dark transitions. Overall, our findings reveal the mechanism by which MdMPK4 controls fruit peel coloration.

Role of Nitric Oxide in Plant Senescence

In plants senescence is the final stage of plant growth and development that ultimately leads to death. Plants experience age-related as well as stress-induced developmental ageing. Senescence involves significant changes at the transcriptional, post-translational and metabolomic levels. Furthermore, phytohormones also play a critical role in the programmed senescence of plants. Nitric oxide (NO) is a gaseous signalling molecule that regulates a plethora of physiological processes in plants. Its role in the control of ageing and senescence has just started to be elucidated. Here, we review the role of NO in the regulation of programmed cell death, seed ageing, fruit ripening and senescence. We also discuss the role of NO in the modulation of phytohormones during senescence and the significance of NO-ROS cross-talk during programmed cell death and senescence.

Plant Salinity Stress Response and Nano-Enabled Plant Salt Tolerance

The area of salinized land is gradually expanding cross the globe. Salt stress seriously reduces the yield and quality of crops and endangers food supply to meet the demand of the increased population. The mechanisms underlying nano-enabled plant tolerance were discussed, including (1) maintaining ROS homeostasis, (2) improving plant's ability to exclude Na+ and to retain K+, (3) improving the production of nitric oxide, (4) increasing α-amylase activities to increase soluble sugar content, and (5) decreasing lipoxygenase activities to reduce membrane oxidative damage. The possible commonly employed mechanisms such as alleviating oxidative stress damage and maintaining ion homeostasis were highlighted. Further, the possible role of phytohormones and the molecular mechanisms in nano-enabled plant salt tolerance were discussed. Overall, this review paper aims to help the researchers from different field such as plant science and nanoscience to better understand possible new approaches to address salinity issues in agriculture.

Editing of the starch branching enzyme gene SBE2 generates high-amylose storage roots in cassava

The production of high-amylose cassava through CRISPR/Cas9-mediated mutagenesis of the starch branching enzyme gene SBE2 was firstly achieved. High-amylose cassava (Manihot esculenta Crantz) is desirable for starch industrial applications and production of healthier processed food for human consumption. In this study, we report the production of high-amylose cassava through CRISPR/Cas9-mediated mutagenesis of the starch branching enzyme 2 (SBE2). Mutations in two targeted exons of SBE2 were identified in all regenerated plants; these mutations, which included nucleotide insertions, and short or long deletions in the SBE2 gene, were classified into eight mutant lines. Three mutants, M6, M7 and M8, with long fragment deletions in the second exon of SBE2 showed no accumulation of SBE2 protein. After harvest from the field, significantly higher amylose (up to 56% in apparent amylose content) and resistant starch (up to 35%) was observed in these mutants compared with the wild type, leading to darker blue coloration of starch granules after quick iodine staining and altered starch viscosity with a higher pasting temperature and peak time. Further ¹H-NMR analysis revealed a significant reduction in the degree of starch branching, together with fewer short chains (degree of polymerization [DP] 15-25) and more long chains (DP>25 and especially DP>40) of amylopectin, which indicates that cassava SBE2 catalyzes short chain formation during amylopectin biosynthesis. Transition from A- to B-type crystallinity was also detected in the starches. Our study showed that CRISPR/Cas9-mediated mutagenesis of starch biosynthetic genes in cassava is an effective approach for generating novel varieties with valuable starch properties for food and industrial applications.

A unique miR775-GALT9 module regulates leaf senescence in Arabidopsis during post-submergence recovery by modulating ethylene and the abscisic acid pathway

The submergence-induced hypoxic condition negatively affects the plant growth and development, and causes early onset of senescence. Hypoxia alters the expression of a number of microRNAs (miRNAs). However, the molecular function of submergence stress-induced miRNAs in physiological or developmental changes and recovery remains poorly understood. Here, we show that miR775 is an Arabidopsis thaliana-specific young and unique miRNA that possibly evolved non-canonically. miR775 post-transcriptionally regulates GALACTOSYLTRANSFERASE 9 (GALT9) and their expression is inversely affected at 24 h of complete submergence stress. The overexpression of miR775 (miR775-Oe) confers enhanced recovery from submergence stress and reduced accumulation of RBOHD and ROS, in contrast to wild-type and MIM775 Arabidopsis shoot. A similar recovery phenotype in the galt9 mutant indicates the role of the miR775-GALT9 module in post-submergence recovery. We predicted that Golgi-localized GALT9 is potentially involved in protein glycosylation. The altered expression of senescence-associated genes (SAG12, SAG29 and ORE1), ethylene signalling (EIN2 and EIN3) and abscisic acid (ABA) biosynthesis (NCED3) pathway genes occurs in miR775-Oe, galt9 and MIM775 plants. Thus, our results indicate the role for the miR775-GALT9 module in post-submergence recovery through a crosstalk between the ethylene signalling and ABA biosynthesis pathways.

Potential Role of Domains Rearranged Methyltransferase7 in Starch and Chlorophyll Metabolism to Regulate Leaf Senescence in Tomato

Deoxyribonucleic acid (DNA) methylation is an important epigenetic mark involved in diverse biological processes. Here, we report the critical function of tomato (Solanum lycopersicum) Domains Rearranged Methyltransferase7 (SlDRM7) in plant growth and development, especially in leaf interveinal chlorosis and senescence. Using a hairpin RNA-mediated RNA interference (RNAi), we generated SlDRM7-RNAi lines and observed pleiotropic developmental defects including small and interveinal chlorosis leaves. Combined analyses of whole genome bisulfite sequence (WGBS) and RNA-seq revealed that silencing of SlDRM7 caused alterations in both methylation levels and transcript levels of 289 genes, which are involved in chlorophyll synthesis, photosynthesis, and starch degradation. Furthermore, the photosynthetic capacity decreased in SlDRM7-RNAi lines, consistent with the reduced chlorophyll content and repression of genes involved in chlorophyll biosynthesis, photosystem, and photosynthesis. In contrast, starch granules were highly accumulated in chloroplasts of SlDRM7-RNAi lines and associated with lowered expression of genes in the starch degradation pathway. In addition, SlDRM7 was activated by aging- and dark-induced senescence. Collectively, these results demonstrate that SlDRM7 acts as an epi-regulator to modulate the expression of genes related to starch and chlorophyll metabolism, thereby affecting leaf chlorosis and senescence in tomatoes.

Chloroplast Protein Tic55 Involved in Dark-Induced Senescence through AtbHLH/AtWRKY-ANAC003 Controlling Pathway of Arabidopsis thaliana

The chloroplast comprises the outer and inner membranes that are composed of the translocon protein complexes Toc and Tic (translocon at the outer/inner envelope membrane of chloroplasts), respectively. Tic55, a chloroplast Tic protein member, was shown to be not vital for functional protein import in Arabidopsis from previous studies. Instead, Tic55 was revealed to be a dark-induced senescence-related protein in our earlier study. To explore whether Tic55 elicits other biological functions, a tic55-II knockout mutant (SALK_086048) was characterized under different stress treatments. Abiotic stress conditions, such as cold, heat, and high osmotic pressure, did not cause visible effects on tic55-II mutant plant, when compared to the wild type (WT). In contrast, senescence was induced in the individually darkened leaves (IDLs), resulting in the differential expression of the senescence-related genes PEROXISOME DEFECTIVE 1 (PED1), BLUE COPPER-BINDING PROTEIN (BCB), SENESCENCE 1 (SEN1), and RUBISCO SMALL SUBUNIT GENE 2B (RBCS2B). The absence of Tic55 in tic55-II knockout mutant inhibited expression of the senescence-related genes PED1, BCB, and SEN1 at different stages of dark adaptation, while causing stimulation of RBCS2B gene expression at an early stage of dark response. Finally, yeast one-hybrid assays located the ANAC003 promoter region with cis-acting elements are responsible for binding to the different AtbHLH proteins, thereby causing the transactivation of an HIS3 reporter gene. ANAC003 was shown previously as a senescence-related protein and its activation would lead to expression of senescence-associated genes (SAGs), resulting in plant senescence. Thus, we propose a hypothetical model in which three signaling pathways may be involved in controlling the expression of ANAC003, followed by expression of SAGs that in turn leads to leaf senescence in Arabidopsis by this study and previous data.

Epigenetic Mechanisms of Senescence in Plants

Senescence is a major developmental transition in plants that requires a massive reprogramming of gene expression and includes various layers of regulations. Senescence is either an age-dependent or a stress-induced process, and is under the control of complex regulatory networks that interact with each other. It has been shown that besides genetic reprogramming, which is an important aspect of plant senescence, transcription factors and higher-level mechanisms, such as epigenetic and small RNA-mediated regulators, are also key factors of senescence-related genes. Epigenetic mechanisms are an important layer of this multilevel regulatory system that change the activity of transcription factors (TFs) and play an important role in modulating the expression of senescence-related gene. They include chromatin remodeling, DNA methylation, histone modification, and the RNA-mediated control of transcription factors and genes. This review provides an overview of the known epigenetic regulation of plant senescence, which has mostly been studied in the form of leaf senescence, and it also covers what has been reported about whole-plant senescence.

MusaATAF2 like protein, a stress-related transcription factor, induces leaf senescence by regulating chlorophyll catabolism and H2 O2 accumulation

NAC transcription factors are known for their diverse role in plants. In this study, we have demonstrated the role of MusaATAF2, a banana NAC transcription factor, in leaf senescence. Its expression gets strongly up-regulated during the early stress responses of drought and high salinity exposure and down-regulated under ABA application, which suggests MusaATAF2 is a stress-related NAC transcription factor. To study the role of MusaATAF2 in banana, we have transformed the banana embryogenic cells with MusaATAF2 coding region and generated transgenic banana plants. Overexpression of MusaATAF2 in banana plants caused yellow leaf phenotype under control condition, suggesting its role as a senescence-associated transcription factor. Transgenic banana leaves exhibited low chlorophyll content and high H₂ O₂ accumulation. Hormone analysis of the leaves demonstrated a higher accumulation of ABA in the transgenic plants than the controls. Transgenic plants overexpressing MusaATAF2 have a higher transcript abundance of two chlorophyll catabolic pathway genes (PAO and HCAR) and lower transcript abundance of ROS scavenging enzymes (TDP, THIO, CAT, APX, and PRXDN) than control. Together, all these analyses indicate that MusaATAF2 induces senescence by inducing chlorophyll degradation and H₂ O₂ accumulation in banana plants and controls its own expression using an ABA-dependent feedback loop.

The NAC Transcription Factor ANAC087 Induces Aerial Rosette Development and Leaf Senescence in Arabidopsis

CmNACP1 mRNA has been shown to move long distance through the phloem in Cucurbita maxima (pumpkin) and through a graft junction. Whereas the phloem transport of several different mRNAs has been documented in other systems as well, its function remains, for most of these RNAs, largely unknown. To gain insight into the possible role of these RNAs, we searched for the closest homologs of CmNACP1 in Arabidopsis, a model plant much more amenable for analysis. A phylogenetic approach using the predicted NAC domain indicated that ANAC059, ANAC092, ANAC079, ANAC100, ANAC046, and ANAC087 form a single clade with CmNACP1. In the present work, we analyzed the possible function of the ANAC087 gene in more detail. The promoter region of this gene directed expression in the vasculature, and also in trichomes, stem, apexes, and developing flowers which supports the notion that ANAC087 and CmNACP1 are orthologs. Overexpression of the ANAC087 gene induced increased branching in inflorescence stem, and also development of ectopic or aerial rosettes in T1 and T2 plants. Furthermore, overexpression of ANAC087 leads to accelerated leaf senescence in 44 days post-germination (dpg). Interestingly, a similar phenotype was observed in plants expressing the ANAC087 gene upstream region, also showing an increase in ANAC087 transcript levels. Finally, the results shown in this work indicate a role for ANAC087 in leaf senescence and also in rosette development.