A Rice NAC Transcription Factor Promotes Leaf Senescence via ABA Biosynthesis
TL;DR: A rice NAC transcription factor, OsNAC2, that participates in ABA-induced leaf senescence and elucidates the transcriptional network of ABA production during leaf senesence in rice is demonstrated.
Abstract: It is well known that abscisic acid (ABA)-induced leaf senescence and premature leaf senescence negatively affect the yield of rice (Oryza sativa). However, the molecular mechanism underlying this relationship, especially the upstream transcriptional network that modulates ABA level during leaf senescence, remains largely unknown. Here, we demonstrate a rice NAC transcription factor, OsNAC2, that participates in ABA-induced leaf senescence. Overexpression of OsNAC2 dramatically accelerated leaf senescence, whereas its knockdown lines showed a delay in leaf senescence. Chromatin immunoprecipitation-quantitative PCR, dual-luciferase, and yeast one-hybrid assays demonstrated that OsNAC2 directly activates expression of chlorophyll degradation genes, OsSGR and OsNYC3. Moreover, ectopic expression of OsNAC2 leads to an increase in ABA levels via directly up-regulating expression of ABA biosynthetic genes (OsNCED3 and OsZEP1) as well as down-regulating the ABA catabolic gene (OsABA8ox1). Interestingly, OsNAC2 is upregulated by a lower level of ABA but downregulated by a higher level of ABA, indicating a feedback repression of OsNAC2 by ABA. Additionally, reduced OsNAC2 expression leads to about 10% increase in the grain yield of RNAi lines. The novel ABA-NAC-SAGs regulatory module might provide a new insight into the molecular action of ABA to enhance leaf senescence and elucidates the transcriptional network of ABA production during leaf senescence in rice.
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TL;DR: The involvement of source strength and stability of the photosynthetic apparatus in this process is emphasized, and a possible role of a perennial plant life strategy for the amelioration of stress-induced senescence is suggested.
Abstract: Senescence is an age-dependent process, ultimately leading to plant death, that in annual crop plants overlaps with the reproductive stage of development. Research on the molecular and biochemical mechanisms of leaf senescence has revealed a multi-layered regulatory network operating to control age-dependent processes. Abiotic stress-induced senescence challenges source-sink relationships and results in significant reduction in crop yields. Although processes associated with plant senescence are well studied, the mechanisms regulating stress-induced senescence are not well known. Here, we discuss the effects of abiotic stress on crop productivity, mechanisms associated with stress-induced senescence, and the possible use of these mechanisms for the generation of plant stress tolerance. We emphasize the involvement of source strength and stability of the photosynthetic apparatus in this process, and suggest a possible role of a perennial plant life strategy for the amelioration of stress-induced senescence.
158 citations
Cites background from "A Rice NAC Transcription Factor Pro..."
...Shen et al., 2017; Mao et al., 2017...
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...In rice, the NAC-type transcription factor OsNAC2 has been shown to regulate ABA-dependent genes and ABA biosynthesis, promoting leaf senescence by directly activating the expression of chlorophyll degradation-associated genes, leading to reduced stress tolerance (Shen et al., 2017; Mao et al., 2017)....
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...Shen et al., 2017; Mao et al., 2017 Chloroplast turnover and chlorophyll metabolism Autophagy-related genes (ATG) mutants Arabidopsis thaliana Over-expression of ATG8f led to sensitivity to stress....
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TL;DR: It is concluded that OsNCED3 mediates seed dormancy, plant growth, abiotic stress tolerance, and leaf senescence by regulating ABA biosynthesis in rice; and may provide a new strategy for improving the quality of crop.
Abstract: Although abscisic acid (ABA) is an important hormone that regulates seed dormancy, stomatal closure, plant development, as well as responses to environmental stimuli, the physiological mechanisms of ABA response to multiple stress in rice remain poorly understood. In the ABA biosynthetic pathway, 9-cis-epoxycarotenoid dioxygenase (NCED) is the key rate-limiting enzyme. Here, we report important functions of OsNCED3 in multi-abiotic stress tolerance in rice. The OsNCED3 is constitutively expressed in various tissues under normal condition, Its expression is highly induced by NaCl, PEG, and H2O2 stress, suggesting the roles for OsNCED3 in response to the multi-abiotic stress tolerance in rice. Compared with wild-type plants, nced3 mutants had earlier seed germination, longer post-germination seedling growth, increased sensitivity to water stress and H2O2 stress and increased stomata aperture under water stress and delayed leaf senescence. Further analysis found that nced3 mutants contained lower ABA content compared with wild-type plants, overexpression of OsNCED3 in transgenic plants could enhance water stress tolerance, promote leaf senescence and increase ABA content. We conclude that OsNCED3 mediates seed dormancy, plant growth, abiotic stress tolerance, and leaf senescence by regulating ABA biosynthesis in rice; and may provide a new strategy for improving the quality of crop.
154 citations
Cites background or methods from "A Rice NAC Transcription Factor Pro..."
...Previous studies have shown that OsNAC2 directly binds to the promoters of the ABA metabolism-related genes OsNCED3, OsZEP1, and OsABA8ox1, which control the production of ABA in plants, and regulate ABA-dependent leaf senescence (Mao et al., 2017)....
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...As expected, transcription levels of the senescence marker genes OsSGR, OsNAP, OsI85, and OsNAC2 in OE1 and OE2 dark-treated leaves were significantly higher compared to those of the wild type, whereas these genes were showed much lower expression in the nced3 lines than in the wild type (Figure 10E)....
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...Dark treatment is an effective method to accelerate leaf senescence and ABA biosynthesis (Mao et al., 2017)....
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...Furthermore, the transcription factors OsNAC2 and OsNAP participated in the aging process dependent on ABA biosynthesis and the leaf-senescence marker genes OsI85 and OsSGR (Chen et al., 2014; Mao et al., 2017)....
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...(E) Relative expression of OsSGR, OsNAP, OsI85, and OsNAC2 genes after 3-day dark treatment in detached nced3-1,2 and OE-1,2 leaves....
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TL;DR: The influence of a NAC transcription factor, SlNAP2 (Solanum lycopersicum NAC-like, activated by Apetala3/Pistillata), that controls both leaf senescence and fruit yield in tomato is described and indicated.
Abstract: Leaf senescence is an essential physiological process in plants that supports the recycling of nitrogen and other nutrients to support the growth of developing organs, including young leaves, seeds, and fruits. Thus, the regulation of senescence is crucial for evolutionary success in wild populations and for increasing yield in crops. Here, we describe the influence of a NAC transcription factor, SlNAP2 (Solanum lycopersicum NAC-like, activated by Apetala3/Pistillata), that controls both leaf senescence and fruit yield in tomato (S. lycopersicum). SlNAP2 expression increases during age-dependent and dark-induced leaf senescence. We demonstrate that SlNAP2 activates SlSAG113 (S. lycopersicum SENESCENCE-ASSOCIATED GENE113), a homolog of Arabidopsis (Arabidopsis thaliana) SAG113, chlorophyll degradation genes such as SlSGR1 (S. lycopersicum senescence-inducible chloroplast stay-green protein 1) and SlPAO (S. lycopersicum pheide a oxygenase), and other downstream targets by directly binding to their promoters, thereby promoting leaf senescence. Furthermore, SlNAP2 directly controls the expression of genes important for abscisic acid (ABA) biosynthesis, S. lycopersicum 9-cis-epoxycarotenoid dioxygenase 1 (SlNCED1); transport, S. lycopersicum ABC transporter G family member 40 (SlABCG40); and degradation, S. lycopersicum ABA 8′-hydroxylase (SlCYP707A2), indicating that SlNAP2 has a complex role in establishing ABA homeostasis during leaf senescence. Inhibiting SlNAP2 expression in transgenic tomato plants impedes leaf senescence but enhances fruit yield and sugar content likely due to prolonged leaf photosynthesis in aging tomato plants. Our data indicate that SlNAP2 has a central role in controlling leaf senescence and fruit yield in tomato.
121 citations
Cites background from "A Rice NAC Transcription Factor Pro..."
...…Yang et al., 2003; Lee et al., 2011; Zhao et al., 2016), the exogenous application of ABA can accelerate chlorophyll degradation (Quiles et al., 1995; Gao et al., 2016), and ABA-deficient mutants display delayed senescence in both rice (Mao et al., 2017) and Arabidopsis (Pourtau et al., 2004)....
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...…family have been reported to be functionally involved in the regulation of leaf senescence in Arabidopsis and other plant species including wheat (Triticum aestivum; Uauy et al., 2006; Zhao et al., 2015), cotton (Gossypium hirsutum; Fan et al., 2015), and rice (Zhou et al., 2013; Mao et al., 2017)....
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TL;DR: It is described that OsNAC2 functions as an upstream integrator of auxin and cytokinin signals that affect CRL and CDK production to regulate cell division during root development.
Abstract: The rice root system is important for growth The crosstalk between auxin and cytokinin mediates root initiation and elongation However, it remains unclear how the transcriptional network upstream of the auxin and cytokinin signalling pathways determines root development Here, we observed that the knockdown of OsNAC2, which encodes a NAC transcription factor, increased the primary root length and the number of crown roots OsNAC2 predominantly expressed in primary root tips, crown roots and lateral root primordia, implying it influences root development Molecular analyses revealed that the expressions of auxin- and cytokinin-responsive genes were affected in OsNAC2-overexpressing (OsNAC2-OX; ON7 and ON11), RNA interference (OsNAC2-RNAi; RNAi25 and RNAi31) and CRISPR/Cas9 plants Additionally, OsNAC2 can directly bind to the promoters of IAA inactivation-related genes (GH36 and GH38), an IAA signalling-related gene (OsARF25), and a cytokinin oxidase gene (OsCKX4) Furthermore, genetic analysis of ON11/osgh36 and RNAi31/osckx4 homozygote confirmed that OsCKX4 and OsGH36 functioned downstream of OsNAC2 The mRNA levels of CROWN ROOTLESS (CRL) genes and cyclin-dependent protein kinase (CDK) genes increased in OsNAC2-RNAi and OsNAC2-cas9 lines while reduced in OsNAC2-OX lines Thus, we describe that OsNAC2 functions as an upstream integrator of auxin and cytokinin signals that affect CRL and CDK production to regulate cell division during root development This novel auxin-OsNAC2-cytokinin model should provide a new insight into the understanding of NAC TFs and crosstalk of auxin and cytokinin pathway, and can be potentially applied in agriculture to enhance rice yields by genetic approaches
113 citations
Cites background from "A Rice NAC Transcription Factor Pro..."
...,2017), senescence (Mao et al., 2017) and programmed cell death (Mao et al....
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...The tandem mass spectrometry analysis confirmed that the endogenous free IAA level was significantly higher in RNAi31 (378 ng/g fresh weight) than in WT (240 ng/g fresh weight) (Figure 4b)....
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...6 and RNAi31*ckx4 homozygote....
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...Furthermore, we observed that the meristem zone length of ON7 and ON11 plants was shorter while that of RNAi25 and RNAi31 plants was longer than the WT plants (Figure 2f)....
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...We previously reported that reduced OsNAC2 expression leads to about 10% increase in the grain yield of RNAi lines (Mao et al., 2017)....
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TL;DR: It is found that exogenous application of melatonin delayed the senescence of Chinese flowering cabbage, accompanied by reduced expression of chlorophyll catabolic and ABA biosynthetic genes, and a lower endogenous ABA level.
Abstract: Melatonin and abscisic acid (ABA) play contrasting roles in regulating leaf senescence in plants. The molecular mechanism underlying the interaction between melatonin and ABA involved in leaf senescence, however, remains poorly defined. Herein, we found that exogenous application of melatonin delayed the senescence of Chinese flowering cabbage, accompanied by reduced expression of chlorophyll catabolic and ABA biosynthetic genes, and a lower endogenous ABA level. Significantly, three nucleus-localized transcriptional activators BrABF1, BrABF4, and BrABI5 were identified, and their expressions were repressed by melatonin. In vitro and in vivo binding experiments revealed that BrABF1, BrABF4, and BrABI5 activated the transcription of a series of ABA biosynthetic and chlorophyll catabolic genes by physically binding to their promoters. Moreover, transient over-expression of BrABF1, BrABF4, and BrABI5 in tobacco leaves induced ABA accumulation and promoted chlorophyll degradation by upregulating tobacco ABA biosynthetic and chlorophyll catabolic genes, resulting in the accelerated leaf senescence. These effects were significantly attenuated by melatonin treatment. Our findings suggest that melatonin-mediated inhibition of leaf senescence involves suppression of ABFs-mediated ABA biosynthesis and chlorophyll degradation. Unraveling of the molecular regulatory mechanism of leaf senescence controlled by ABA and melatonin expands our understanding of the regulation of this phenomenon and offers potentially more effective molecular breeding strategies for extending the shelf-life of Chinese flowering cabbage.
108 citations
References
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TL;DR: A new model for ABA action has been proposed and validated, in which the soluble PYR/PYL/RCAR receptors function at the apex of a negative regulatory pathway to directly regulate PP2C phosphatases, which in turn directly regulate SnRK2 kinases.
Abstract: Abscisic acid (ABA) regulates numerous developmental processes and adaptive stress responses in plants. Many ABA signaling components have been identified, but their interconnections and a consensus on the structure of the ABA signaling network have eluded researchers. Recently, several advances have led to the identification of ABA receptors and their three-dimensional structures, and an understanding of how key regulatory phosphatase and kinase activities are controlled by ABA. A new model for ABA action has been proposed and validated, in which the soluble PYR/PYL/RCAR receptors function at the apex of a negative regulatory pathway to directly regulate PP2C phosphatases, which in turn directly regulate SnRK2 kinases. This model unifies many previously defined signaling components and highlights the importance of future work focused on defining the direct targets of SnRK2s and PP2Cs, dissecting the mechanisms of hormone interactions (i.e., cross talk) and defining connections between this new negative regulatory pathway and other factors implicated in ABA signaling.
2,359 citations
Additional excerpts
...ABA has vital function in stress responses and regulates various plant developments, e.g. seed maturation and dormancy, organ abscission, and leaf senescence (Chandler and Robertson, 1994; Cutler et al., 2010)....
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...seed maturation and dormancy, organ abscission, and leaf senescence (Chandler and Robertson, 1994; Cutler et al., 2010)....
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...ABA is generally considered as a senescence initiator (Cutler et al., 2010)....
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TL;DR: Identification of ABA metabolic genes has revealed that multiple metabolic steps are differentially regulated to fine-tune the ABA level at both transcriptional and post-transcriptional levels.
Abstract: The level of abscisic acid (ABAabscisic acid) in any particular tissue in a plant is determined by the rate of biosynthesis and catabolism of the hormone. Therefore, identifying all the genes involved in the metabolism is essential for a complete understanding of how this hormone directs plant growth and development. To date, almost all the biosynthetic genes have been identified through the isolation of auxotrophic mutants. On the other hand, among several ABA catabolic pathways, current genomic approaches revealed that Arabidopsis CYP707A genes encode ABA 8′-hydroxylases, which catalyze the first committed step in the predominant ABA catabolic pathway. Identification of ABA metabolic genes has revealed that multiple metabolic steps are differentially regulated to fine-tune the ABA level at both transcriptional and post-transcriptional levels. Furthermore, recent ongoing studies have given new insights into the regulation and site of ABA metabolism in relation to its physiological roles.
1,890 citations
Additional excerpts
...In higher plants, the level of ABA is finely controlled by the balance between the rates of ABA biosynthesis and catabolism (Nambara and Marion-Poll, 2005)....
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TL;DR: In this article, a series of plasmid vectors for transient gene expression using Agrobacterium, infiltrated into Nicotiana benthamiana leaves, are described and compared to conventional binary vectors for stable transformation such as transformation selection genes.
Abstract: We describe novel plasmid vectors for transient gene expression using Agrobacterium, infiltrated into Nicotiana benthamiana leaves. We have generated a series of pGreenII cloning vectors that are ideally suited to transient gene expression, by removing elements of conventional binary vectors necessary for stable transformation such as transformation selection genes. We give an example of expression of heme-thiolate P450 to demonstrate effectiveness of this system. We have also designed vectors that take advantage of a dual luciferase assay system to analyse promoter sequences or post-transcriptional regulation of gene expression. We have demonstrated their utility by co-expression of putative transcription factors and the promoter sequence of potential target genes and show how orthologous promoter sequences respond to these genes. Finally, we have constructed a vector that has allowed us to investigate design features of hairpin constructs related to their ability to initiate RNA silencing, and have used these tools to study cis-regulatory effect of intron-containing gene constructs. In developing a series of vectors ideally suited to transient expression analysis we have provided a resource that further advances the application of this technology. These minimal vectors are ideally suited to conventional cloning methods and we have used them to demonstrate their flexibility to investigate enzyme activity, transcription regulation and post-transcriptional regulatory processes in transient assays.
1,197 citations
TL;DR: The biological and molecular functions of the NAC family are summarized, paying particular attention to the intricate regulation of NAC protein level and localization, and to the first indications of Nac participation in transcription factor networks.
1,195 citations
Additional excerpts
...Thus, we checked whether CACG sequences exist in the promoters of these five target genes....
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...S5), which indicated CACG might also be the binding motif of OsNAC2....
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...Previous work has defined the 4-bp core sequence of the NAC binding motif as CACG (Olsen et al., 2005)....
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...NAC proteins, which belong to the CUC subfamily, have been demonstrated to play a pivotal part in plant development (Olsen et al., 2005), stress responses (Puranik et al....
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...NAC binding motif CACG searching....
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TL;DR: Results indicate that both the rd22BP1 (MYC) and ATMYB2 (MYB) proteins function as transcriptional activators in the dehydration- and ABA-inducible expression of the r d22 gene.
Abstract: In Arabidopsis, the induction of a dehydration-responsive gene, rd22, is mediated by abscisic acid (ABA) and requires protein biosynthesis for ABA-dependent gene expression. Previous experiments established that a 67-bp DNA fragment of the rd22 promoter is sufficient for dehydration- and ABA-induced gene expression and that this DNA fragment contains two closely located putative recognition sites for the basic helix-loop-helix protein MYC and one putative recognition site for MYB. We have carefully analyzed the 67-bp region of the rd22 promoter in transgenic tobacco plants and found that both the first MYC site and the MYB recognition site function as cis-acting elements in the dehydration-induced expression of the rd22 gene. A cDNA encoding a MYC-related DNA binding protein was isolated by DNA-ligand binding screening, using the 67-bp region as a probe, and designated rd22BP1. The rd22BP1 cDNA encodes a 68-kD protein that has a typical DNA binding domain of a basic region helix-loop-helix leucine zipper motif in MYC-related transcription factors. The rd22BP1 protein binds specifically to the first MYC recognition site in the 67-bp fragment. RNA gel blot analysis revealed that transcription of the rd22BP1 gene is induced by dehydration stress and ABA treatment, and its induction precedes that of rd22. We have reported a drought- and ABA-inducible gene that encodes the MYB-related protein ATMYB2. In a transient transactivation experiment using Arabidopsis leaf protoplasts, we demonstrated that both the rd22BP1 and ATMYB2 proteins activate transcription of the rd22 promoter fused to the beta-glucuronidase reporter gene. These results indicate that both the rd22BP1 (MYC) and ATMYB2 (MYB) proteins function as transcriptional activators in the dehydration- and ABA-inducible expression of the rd22 gene.
1,068 citations
"A Rice NAC Transcription Factor Pro..." refers background in this paper
...The recognition site of MYC2 appears to function as both positive and negative regulator of the expression of the MYC2 promoter-GUS fusion gene (Abe et al., 1997)....
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