Knockout of the lignin pathway gene BnF5H decreases the S/G lignin composition ratio and improves S. sclerotiorum resistance in B. napus

Ferulate-5-hydroxylase is a key enzyme involved in the conversion of the guaiacyl monolignol to the syringyl monolignol in angiosperms. The monolignol ratio has been proposed to affect biomass recalcitrance and the resistance to plant disease. Stem rot caused by the fungus Sclerotinia sclerotiorum in Brassica napus causes severe losses in its production. To date, there is no information about the effect of the lignin monomer ratio on the resistance to Sclerotinia sclerotiorum in Brassica napus. Four dominantly expressed ferulate-5-hydroxylase genes were concertedly knocked out by CRISPR/Cas9 in Brassica napus, and three mutant lines were generated. The S/G lignin compositional ratio was decreased compared to that of the wild type based on the results of Mӓule staining and 2D-NMR profiling in KO-7. The resistance to Sclerotinia sclerotiorum in stems and leaves increased for the three f5h mutant lines compared with wild type. Furthermore, we found that the stem strength of f5h mutant lines was significantly increased. Overall, we demonstrate for the first time that decreasing the S/G ratio by knocking out of the F5H gene improves Sclerotinia sclerotiorum resistance in Brassica napus and increases stem strength. This article is protected by copyright. All rights reserved.