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

Abstract

Ferulate-5-hydroxylase (F5H) is a key enzyme involved in the conversion of the guaiacyl monolignol (G-monolignol) to the syringyl monolignol (S-monolignol) in angiosperms. The monolignol ratio has been proposed to affect biomass recalcitrance and the resistance to plant disease. Sclerotinia sclerotiorum (S. sclerotiorum) stem rot of Brassica napus (B. napus) causes heavy damage in oilseed rape production. To date, there is no information about the effect of the lignin monomer ratio on the resistance to S. sclerotiorum in B. napus. Four dominantly expressed BnF5H genes were knocked out by CRISPR/Cas9 simultaneously in B. napus, and the f5h mutant KO-7 was generated. The S/G lignin composition ratio was decreased compared to that of the wild type (WT) based on the results of Mӓule staining and 2D-NMR profiling. The resistance to S. sclerotiorum in stems and leaves increased in KO-7. Furthermore, we found that the stem strength of KO-7 was significantly increased compared to that of the WT. Collectively, for the first time, we demonstrate that knockout of the lignin pathway gene F5H decreases the S/G ratio, improves S. sclerotiorum resistance in B. napus, and increases stem strength.

Lignin and Its Pathway-Associated Phytoalexins Modulate Plant Defense against Fungi

“…The F5H is the third P450-dependent protein that regulates lignin biosynthesis. It catalyzes S-monolignol from G-monolignol through 5-hydroxylation of coniferaldehyde and coniferyl alcohols [ 85 , 86 ]. The role of F5H in lignin production is proposed to be thwarted by microRNA from Bacopa monnieri ( Bm-miR172c-5p ) which cleaves F5H and interferes with lignin elicitation [ 87 ].…”

“…A CRISPR/Cas9-mediated knockout of four F5H ( ko-7 ) genes from Brassica napus (oilseed rape) reduced the syringyl:guaiacyl monolignol ratio (S: G). The ko-7 mutant developed resistance against pathogenic Sclerotinia sclerotiorum (stem rot) through cell wall fortification [ 86 ]. F5H also confers immunity against parasitic plants.…”