Lignin Composition and Timing of Cell Wall Lignification Are Involved in Resistance to Stem Rot Caused by .

Sclerotinia stem rot (SSR) is an economically and globally significant disease in oilseed rape () caused by the necrotrophic ascomycete . This study explored the role of cell wall reinforcement by lignin as a relevant factor for effective plant defense against attack by this pathogen. Expression of key genes in the phenylpropanoid pathway and the induced synthesis of lignin in infected stem tissues were investigated in a study comparing a susceptible ('Loras') and a moderately resistant cultivar ('Zhongyou 821' [ZY821]). Data revealed an earlier and more rapid defense activation in ZY821 through upregulation of transcript levels of genes related to key steps in the phenylpropanoid pathway associated with increased lignin deposition in the resistant genotype. Expression level of , encoding a cinnamyl alcohol dehydrogenase, responsible for conversion of monolignol to lignin, was more rapidly upregulated in ZY821 than 'Loras'. The similar expression pattern of and the gene , encoding for ferulate-5-hydroxylase, which catalyzes the synthesis of syringyl (S) lignin precursors, suggests that is involved in S lignin formation. Histological observations confirmed these results, showing an earlier increase of S lignin deposition in the infected resistant genotype. Deposition of guaiacyl lignin was detected in both genotypes and is thus considered a component of basal, cultivar-independent defense response of to stem rot. The results indicate the importance of cell wall modification for quantitative stem rot resistance by responses in the phenylpropanoid metabolism generating distinct lignin types on different temporal scales.