[Show abstract][Hide abstract] ABSTRACT: Plants have evolved an elaborate signaling network to ensure an appropriate level of immune response to meet the differing demands of developmental processes. Previous research has demonstrated that DELLA proteins physically interact with JAZ1 and dynamically regulate the interaction of the gibberellic acid (GA) and jasmonic acid (JA) signaling pathways. However, whether and how the JAZ1-DELLA regulatory node is regulated at the transcriptional level in plants under normal growth conditions or during pathogen infection is not known. Here, we demonstrate multiple functions of Gossypium barbadense GbWRKY1 in the plant defense response and during development. Although GbWRKY1 expression is induced rapidly by MeJA and infection by Verticillium dahliae, our results show that GbWRKY1 is a negative regulator of the JA-mediated defense response and plant resistance to the pathogens Botrytis cinerea and V. dahliae. Under normal growth conditions, GbWRKY1-overexpressing lines displayed GA-associated phenotypes, including organ elongation and early flowering, coupled with the downregulation of the putative targets of DELLA. We show that the GA-related phenotypes of GbWRKY1-overexpressing plants depend on the constitutive expression of Gossypium hirsutum GhJAZ1. We also show that GhJAZ1 can be trans-activated by GbWRKY1 through TGAC core sequences, and the adjacent sequences of this binding site are essential for binding specificity and affinity to GbWRKY1 as revealed by dual-luciferase reporter assays and electrophoretic mobility shift assays. In summary, our data suggest that GbWRKY1 is a critical regulator mediating the plant defense-to-development transition during V. dahliae infection by activating JAZ1 expression.
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Overexpression of a cotton defense-related gene GbWRKY1 in Arabidopsis resulted in modification of the root system by enhanced auxin sensitivity to positively regulate the Pi starvation response. GbWRKY1 was a cloned WRKY transcription factor from Gossypium barbadense, which was firstly identified as a defense-related gene and showed moderate similarity with AtWRKY75 from Arabidopsis thaliana. Overexpression of GbWRKY1 in Arabidopsis resulted in attenuated Pi starvation stress symptoms, including reduced accumulation of anthocyanin and impaired density of lateral roots (LR) in low Pi stress. The study also indicated that overexpression of GbWRKY1 caused plants constitutively exhibited Pi starvation response including increased development of LR, relatively high level of total P and Pi, high expression level of some high-affinity Pi transporters and phosphatases as well as enhanced accumulation of acid phosphatases activity during Pi-sufficient. It was speculated that GbWRKY1 may act as a positive regulator in the Pi starvation response as well as AtWRKY75. GbWRKY1 probably involves in the modulation of Pi homeostasis and participates in the Pi allocation and remobilization but do not accumulate more Pi in Pi-deficient condition, which was different from the fact that AtWRKY75 influenced the Pi status of the plant during Pi deprivation by increasing root surface area and accumulation of more Pi. Otherwise, further study suggested that the overexpression plants were more sensitive to auxin than wild-type and GbWRKY1 may partly influence the LPR1-dependent (low phosphate response 1) Pi starvation signaling pathway and was putatively independent of SUMO E3 ligase SIZ1 and PHR1 (phosphate starvation response 1) in response to Pi starvation.
[Show abstract][Hide abstract] ABSTRACT: The incompatible pathosystem between resistant cotton (Gossypium barbadense cv. 7124) and Verticillium dahliae strain V991 was used to study the cotton transcriptome changes after pathogen inoculation by RNA-Seq. Of 32,774 genes detected by mapping the tags to assembly cotton contigs, 3442 defence-responsive genes were identified. Gene cluster analyses and functional assignments of differentially expressed genes indicated a significant transcriptional complexity. Quantitative real-time PCR (qPCR) was performed on selected genes with different expression levels and functional assignments to demonstrate the utility of RNA-Seq for gene expression profiles during the cotton defence response. Detailed elucidation of responses of leucine-rich repeat receptor-like kinases (LRR-RLKs), phytohormone signalling-related genes, and transcription factors described the interplay of signals that allowed the plant to fine-tune defence responses. On the basis of global gene regulation of phenylpropanoid metabolism-related genes, phenylpropanoid metabolism was deduced to be involved in the cotton defence response. A closer look at the expression of these genes, enzyme activity, and lignin levels revealed differences between resistant and susceptible cotton plants. Both types of plants showed an increased level of expression of lignin synthesis-related genes and increased phenylalanine-ammonia lyase (PAL) and peroxidase (POD) enzyme activity after inoculation with V. dahliae, but the increase was greater and faster in the resistant line. Histochemical analysis of lignin revealed that the resistant cotton not only retains its vascular structure, but also accumulates high levels of lignin. Furthermore, quantitative analysis demonstrated increased lignification and cross-linking of lignin in resistant cotton stems. Overall, a critical role for lignin was believed to contribute to the resistance of cotton to disease.