High resolution profiling of gene expression during probenazole (PBZ) treatment in Arabidopsis
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ABSTRACT: Leaf senescence is a developmentally programmed event, which is also regulated by several phytohormones such as SA. SA has been shown to regulate the expression of many genes during leaf senescence, the fact that the mutants defective in SA biosynthesis and signaling have negligible senescence-related phenotypes makes it difficult to evaluate the exact role of SA in regulating leaf senescence. We have previously shown that probenazole (PBZ) is able to induce endogenous SA biosynthesis when applied by root drenching. We also detected an accelerated leaf yellowing phenotype about two weeks after PBZ treatment. Analysis of PBZ response genes identifies several MAPKs genes may be involved in SA induced senescence signaling pathway. We used microarrays to detail the global programme of gene expression underlying probenazole (PBZ) treatment in Arabidopsis and identified distinct classes of MAPKs genes during this process.
Project description:Leaf senescence is a developmental process designed for nutrient recycling and relocation to maximize growth competence and reproductive capacity of plants. Thus, plants integrate developmental and environmental signals to precisely control senescence. However, it remains largely elusive as to how plants coordinate genetic, epigenetic, and metabolic pathways for the regulation of senescence. To genetically dissect the complex regulatory mechanism underlying leaf senescence, we identified an early leaf senescence mutant, rse1. RSE1 encodes a putative glycosyltranferase. Loss-of-function mutations in RSE1 resulted in precocious leaf yellowing and up-regulation of senescence maker genes, indicating enhanced leaf senescence. Transcriptome analysis revealed that salicylic acid (SA) and defense signaling cascades were activated in rse1 prior to the onset of leaf senescence. In agreement with the phenotypes, we found that SA accumulation was significantly increased in rse1. We also discovered that the rse1 phenotypes are dependent on SA-INDUCTION DEFICIENT 2 (SID2), indicating a role of SA in accelerated leaf senescence in rse1. Furthermore, RSE1 protein was localized to the cell walls, and rse1 displayed increased glucose contents in the cell walls, implying a possible link between the cell walls and RSE1 function. Together, we show that RSE1 negatively modulate leaf senescence through an SID2-dependent SA signaling pathway.
Project description:Phytohormones control many vital biological processes within plants, including growth and development, senescence, seed setting, fruit ripening and innate immunity. These biological processes are controlled by specific combinations of multiple phytohormones. The three main phytohormones involved in plant innate immunity are salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). SA is produced in response to biotrophic and hemibiotrophic pathogens. Whereas, JA and ET are produced in response to necrotrophic pathogens. Pseudomonas aeruginosa is found ubiquitously within the environment, and has been shown to participate in both beneficial and pathogenic interactions with host plants depending on bacterial strain and environment. In this study, we found that Brassica napus (canola) seedlings infected with P. aeruginosa strain PA14 displayed symptoms of disease and had significant weight loss in both root and shoot. Our transcriptomic data revealed that many molecular processes involved in plant innate immunity were upregulated, whereas photosynthesis was downregulated.
Project description:Abscisic acid (ABA) is a phytohormone that promotes leaf senescence in response to environmental stress. We previously identified methyl CpG-binding domain 10 (MBD10) as a phosphoprotein that becomes differentially phosphorylated after ABA treatment in Arabidopsis. ABA-induced leaf senescence was delayed in mbd10 knockout plants but accelerated in MBD10-overexpressing plants, suggesting that MBD10 positively regulates ABA-induced leaf senescence. ABA-induced phosphorylation of MBD10 occurs in planta on Thr-89, and our results demonstrated that Thr-89 phosphorylation is essential for MBD10’s function in leaf senescence. The in vivo phosphorylation of Thr-89 in MBD10 was significantly downregulated in a quadruple mutant of group C MAPKs (mpk1/2/7/14), and group C MAPKs directly phosphorylated MBD10 in vitro.
Project description:Leaf senescence is a highly coordinated and complicated process with the integration of numerous internal and environmental signals. Salicylic acid (SA) and reactive oxygen species (ROS) are two well-defined inducers of leaf senescence, whose contents progressively and inter-dependently increase during leaf senescence via a yet unknown mechanism. Here, we have characterized a newly identified positive regulator of leaf senescence, WRKY75, and demonstrated that knock-down or knock-out of WRKY75 delays, while over-expression of WRKY75 accelerates age-dependent leaf senescence. The WRKY75 transcription is induced by age, SA, H2O2, as well as multiple plant hormones. Meanwhile, WRKY75 is able to promote SA production by inducing the transcription of SA INDUCTION-DEFICIENT 2 (SID2), and suppress H2O2 scavenging partly by repressing the transcription of CATALASE 2 (CAT2). Genetic analysis reveals that the SID2 mutation or an increase of catalase activity rescues the precocious leaf senescence phenotype evoked by WRKY75 over-expression. Based on these results, we propose a “tripartite amplification loop” model in which WRKY75, SA and ROS undergo a gradual but self-sustained rise driven by three interlinked positive feedback regulations. This tripartite amplification loop provides a molecular framework connecting the upstream signals, such as age, ethylene, JA and ABA, to the downstream regulatory network executed by those SA-responsive and H2O2-responsive transcription factors during leaf senescence.
Project description:A transcriptomic time-course study was performed on the senescence process in flag leaves of the spring wheat cultivar Bobwhite grown in the green-house. Leaf samples were harvested at eight time-points from the time of ear emergence until 50% yellowing of the harvested leaf sample.
Project description:Several phytohormones and other small molecules have been demonstrated to be involved in iron (Fe) homeostasis. However, how salicylic acid (SA), an essential hormone in plant immunity and defense responses, participates in Fe-deficiency responses in plants is largely unknown. Here, we took advantage of a SA biosynthesis defect mutant phytoalexin deficient 4 (pad4: T-DNA Salk_089936) to explore the possible effects of endogenous SA on the morphological and physiological responses to Fe deprivation. Under a Fe-deficiency treatment, Col-0 showed more severe leaf chlorosis and root growth inhibition compared with the pad4 mutant. The soluble Fe concentrations were significant higher in pad4 than Col-0 under the Fe-deficiency treatment, suggesting that a mutation in the PAD4 gene may alleviate the Fe-deficiency-induced symptoms by regulating the soluble Fe concentrations. Furthermore, a SA signaling maker line (PR1promoter: GUS) was used to investigate how Fe deficiency affects endogenous SA biosynthesis and metabolism. The data showed that Fe deficiency significantly induced SA accumulation in Col-0, and the loss function of PAD4 blocked this process. The requirement of endogenous SA accumulation for Fe-deficiency responses was confirmed using a series of SA biosynthetic mutants and transgenic lines.
Project description:SA0420 is a stable rice (Oryza sativa L.) mutant exhibits multiple traits including a leaf-tip yellowing (YLT), a taro fragrance (or aroma, A), a reduced panicle number (PN), spikelet number (SN), plant height (PH), days to heading (DH), filled grain weight (FGW), and fertility rate (FR), different from those of a local cultivar TNG67. Correlation analysis on F2 progenies of SA0420 and TNG67 revealed that except for aroma which is inheritated independently, phenotypes including YLT, PN, SN, PH, and FGW are tightly associated with each others, indicating a control simultaneously by pleotropic gene. Among those phenotypes, YLT appears the earliest at vegetative stage, therefore may act as a predisposing factor that give rise to other phenotypes. Genetic analysis suggested that YLT is controlled by a single recessive gene. By analyzing the recombinant inbreed lines (RILs) that produce YLT and normal green (G) progenies in a 1:3 ratio, the phenotypes associated with YLT were further confirmed. To investigate the molecular events of leaf-tip yellowing, microarray analyses were performed to compare the gene expression profiles between YLT and G plants of RILs. Clustering of genes according to their involved metabolic pathways revealed that various photosynthesis and carbon fixation gene expressions are lower (~55~75%) in YLT than in G plants, consistent with the observation that photosynthesis rate of SA0420 was only 60% to that of TNG67. Moreover, higher expressions of oxidative phosphorylation-related genes indicated that not only the reduced synthesis rate but also the elevated energy consumptions may synergistically decrease the growth vigor of SA0420. Dissection of the mature leaf revealed that chlorophyll is drastically reduced in the leaf-tip of SA0420 while carotenoids remain stable. This explains the appearance of leaf-tip yellowing and recall an analogy of early senescence. Indeed, many senescence-associated genes (SAG) were found to be up-regulated in SA0420. Experiment Overall Design: To investigate the molecular events of leaf-tip yellowing, microarray analyses were performed to compare the gene expression profiles between YLT and G plants of RILs.
Project description:1. Comparison of two near isogenic lines between which the genome differs only for the region of the leaf-yellowing QTL Y3-4 on chromosome III.<br> Experiment description: <br><br> The lines HIF404-Sha and HIF404-Bay were grown on 3 mM nitrate in growth chamber according to Loudet et al . (2002, TAG 104:1173-84) until phenotypic yellowing symptoms differed between them. Plants were collected 49 days after sowing.<br><br> 2. Comparison of sugar effect on the leaf senescence progress using three RIL from the Bay-0 x shahdara population that exhibited differential leaf yellowing symptoms.<br> Experiment description: The recombinant inbred lines RIL310 (hypersenescing and early-senescing), RIL232 (early--senescing) et RIL045 (late-senescing) were grown in petri dishes (4,7 mM Nitrogen, with (LNG) or without (LN) glucose 2% until some difference of Fv/Fm trait can be observed (Wingler et al. 2004, New Phytol, 161 : 781-789). Growth experiments were performed in A. Wingler lab, University College of London.
Project description:Leaf senescence can be triggered by jasmonic acid (JA) and darkness. There are scattered reports about JA and dark-induced senescence, respectively. While the precise regulatory mechanisms that integrate these two factors to initiate and regulate leaf senescence have not been identified. Here, we report a transcriptional regulating module centered on novel WRKY transcription factor that is responsible for both JA and dark-induced leaf senescence in tomato. The expression levels of SlWRKY37 together with the master transcription factor in JA signaling SlMYC2 could be significantly induced by both MeJA and dark treatments. SlMYC2 directly binds to the promoter of SlWRKY37 to active its expression. Knock out of SlWRKY37 inhibited JA and dark-induced leaf senescence. Transcriptome analysis revealed 1312 differentially expressed genes between slwrky37-CR and SlWRKY37-OE, including genes involved in JA synthesis as well as several senescence-associated genes (SAGs). We characterized SlWRKY53 and SlSGR1 as direct transcriptional targets of SlWRKY37 to regulate leaf senescence. Moreover, SlWRKY37 interacts with SlVQ7 protein in vivo and the interaction enhances its binding ability to the promoters and transcriptional activation to downstream target genes. In addition, SlWRKY37 is phosphorylated at the post-translational level. Phosphorylation of SlWRKY37 is essential for its protein interaction and transcriptional activation, indicating phosphorylation modification has a great effect on the function of SlWRKY37 protein. Our study reveals the physiological and molecular functions of SlWRKY37 in leaf senescence and offered a target gene to retard leaf yellowing by reducing the sensitivity to internal and external senescence signal such as JA and darkness.
Project description:SA0420 is a stable rice (Oryza sativa L.) mutant exhibits multiple traits including a leaf-tip yellowing (YLT), a taro fragrance (or aroma, A), a reduced panicle number (PN), spikelet number (SN), plant height (PH), days to heading (DH), filled grain weight (FGW), and fertility rate (FR), different from those of a local cultivar TNG67. Correlation analysis on F2 progenies of SA0420 and TNG67 revealed that except for aroma which is inheritated independently, phenotypes including YLT, PN, SN, PH, and FGW are tightly associated with each others, indicating a control simultaneously by pleotropic gene. Among those phenotypes, YLT appears the earliest at vegetative stage, therefore may act as a predisposing factor that give rise to other phenotypes. Genetic analysis suggested that YLT is controlled by a single recessive gene. By analyzing the recombinant inbreed lines (RILs) that produce YLT and normal green (G) progenies in a 1:3 ratio, the phenotypes associated with YLT were further confirmed. To investigate the molecular events of leaf-tip yellowing, microarray analyses were performed to compare the gene expression profiles between YLT and G plants of RILs. Clustering of genes according to their involved metabolic pathways revealed that various photosynthesis and carbon fixation gene expressions are lower (~55~75%) in YLT than in G plants, consistent with the observation that photosynthesis rate of SA0420 was only 60% to that of TNG67. Moreover, higher expressions of oxidative phosphorylation-related genes indicated that not only the reduced synthesis rate but also the elevated energy consumptions may synergistically decrease the growth vigor of SA0420. Dissection of the mature leaf revealed that chlorophyll is drastically reduced in the leaf-tip of SA0420 while carotenoids remain stable. This explains the appearance of leaf-tip yellowing and recall an analogy of early senescence. Indeed, many senescence-associated genes (SAG) were found to be up-regulated in SA0420. Keywords: rice (Oryza sativa), yellow and green leaves, molecular functions, signal-microarray, vegetative stage