Lignin metabolism has a central role in the resistance of cotton to the wilt fungus Verticillium dahliae as revealed by RNA-Seq-dependent transcriptional analysis and histochemistry

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.

Cotton WRKY1 Mediates the Plant Defense-to-Development Transition during Infection of Cotton byVerticillium dahliaeby ActivatingJASMONATE ZIM-DOMAIN1Expression

“…[See online article for color version of this figure. ] potato (Solanum tuberosum; Zhou et al, 2006;Klosterman et al, 2009). Typical symptoms caused by V. dahliae include leaf necrosis, premature defoliation, altered flowering time, and severe growth stunting (Veronese et al, 2003;Fradin et al, 2009;Xu et al, 2011b). Recent studies have identified signaling pathways that play essential roles in cotton resistance to V. dahliae (Xu et al, 2011b;Gao et al, 2013;Zhang et al, 2013), but how plants orchestrate development under V. dahliae infection remains elusive.…”

“…Typical symptoms caused by V. dahliae include leaf necrosis, premature defoliation, altered flowering time, and severe growth stunting (Veronese et al, 2003;Fradin et al, 2009;Xu et al, 2011b). Recent studies have identified signaling pathways that play essential roles in cotton resistance to V. dahliae (Xu et al, 2011b;Gao et al, 2013;Zhang et al, 2013), but how plants orchestrate development under V. dahliae infection remains elusive. By mining genes that are expressed differentially in response to V. dahliae from the cotton '7124', the WRKY transcription factor gene GbWRKY1 was identified as putatively functioning in the phosphate starvation and resistance response (Xu et al, 2011a(Xu et al, , 2012b.…”

“…To determine whether GbWRKY1 could negatively affect the JA-mediated defense response, we checked the expression of cotton pathogenesis-related protein GbPR4, which is a molecular marker of the JA signaling pathway in cotton (Xu et al, 2011b;Gao et al, 2013). Quantitative reverse transcription (qRT)-PCR analysis demonstrated that the expression of GbPR4 was highly induced by MeJA in the GbWRKY1-silencing cotton line Ci2, while only a slight up-regulation of GbPR4 transcript could be found in the GbWRKY1-overexpressing cotton line COV4 after MeJA treatment (Fig.…”

“…The V. dahliae infection assays were performed by root dipping with spore suspension (2 3 10 5 spores mL 21 ) as described previously (Xu et al, 2011b;Gao et al, 2013). The disease index (%) was measured to examine the susceptibility to V. dahliae as described previously (Xu et al, 2012a).…”

Proteomic and Virus-induced Gene Silencing (VIGS) Analyses Reveal That Gossypol, Brassinosteroids, and Jasmonic acid Contribute to the Resistance of Cotton to Verticillium dahliae

“…Production of phytoalexins, including terpenoids, and phenylpropanoid substances, is induced quickly in cotton on infection by V. dahliae (18,19). Gossypol is one of the most important sesquiterpene phytoalexin, which exists specifically in cotton and plays a crucial role in the defense against the invasion of pathogens and insects (20).…”