Identification and Characterization of Cinnamyl Alcohol Dehydrogenase Encoding Genes Involved in Lignin Biosynthesis and Resistance to in Upland Cotton ( L.).

Verticillium wilt, caused by the soil-borne fungus , is one of the most devastating diseases in cotton ( spp.). Lignin in the cell wall forms a physical barrier to inhibit pathogen invasion, and defense-induced lignification reinforces secondary cell wall to prevent pathogens from further spreading. Cinnamyl alcohol dehydrogenases (CADs) catalyze the production of three main monolignols, -coumaryl- (H), coniferyl- (G), and sinapyl-alcohols (S), which are the fundamental blocks of lignin. Here, we identified genes in , analyzed their expression profiles in cotton leaf, stem, and root from different developmental stages, and selected , , and , which were consistently induced by inoculation in cultivars resistant or susceptible to . On the basis of confirmation of the enzymatic activity of the three proteins in generation of the three monolignols, we used virus-induced gene silencing (VIGS) to investigate the effects of silencing of , , or on resistance to as well as on deposition and the composition of lignin. Silencing each of the three s impaired the defense-induced lignification and salicylic acid biosynthesis in stem, and compromised resistance to . Moreover, our study showed that silencing the three s severely affected the biosynthesis of S-lignin, leading to a decrease of the syringyl/guaiacyl (S/G) ratio. Heterogeneous overexpression of , , or in enhanced disease resistance. Taken together, our study demonstrates a role of the three s in defense-induced lignin biosynthesis and resistance to in .