Knockout of the lignin pathway gene BnF5H decreases the S/G lignin compositional ratio and improves Sclerotinia sclerotiorum resistance in Brassica napus

Abstract

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 S. sclerotiorum in B. napus. Four dominantly expressed ferulate‐5‐hydroxylase genes were concertedly knocked out by CRISPR/Cas9 in B. 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 S. sclerotiorum in stems and leaves increased for the three f5h mutant lines compared with WT. 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 S. sclerotiorum resistance in B. napus and increases stem strength.

QTL Identification for Stem Fiber, Strength and Rot Resistance in a DH Population from an Alien Introgression of Brassica napus

“…We found that the breaking strength (F) was significantly positively correlated with ADL, and significantly negatively correlated with SG and stem disease susceptibility ( Supplementary Table S2 ), indicating that increasing the ADL content, especially the G proportion, could enhance the stem strength and disease resistance. G monolignol played a vital role in stem strength, which supported the result that decreasing the S/G ratio could improve the S. sclerotiorum resistance in B. napus and increase stem strength [ 2 , 5 ]. Therefore, we could increase the ADL content and alter ADL composition to improve stem strength, lodging and S. sclerotiorum resistance in future breeding programs.…”

“…Rapeseed ( Brassica napus ) is a widely grown crop that is used as vegetable oil for human, biodiesel energy for industry and feeding protein for animals. Fiber-related components, including lignin, cellulose (Cel) and hemicellulose (Hem), have played important roles in stem lodging [ 1 , 2 ], biomass digestibility [ 3 ] and Sclerotinia sclerotiorum (causing stem rot) resistance (SSR) [ 4 , 5 ] in B . napus .…”

“…Moreover, the S/G monolignol ratio was significantly negatively correlated with lodging resistance and stem disease susceptibility. A recent study proved that decreasing the S/G ratio by knocking out of the lignin pathway gene, BnF5H , could improve the S. sclerotiorum resistance and increase stem strength [ 5 ].…”

“…Sclerotinia sclerotiorum is a necrotrophic lifestyle fungal pathogen, which can cause 0–20% of yield loss every year in B. napus and can reach up to 80% in severely infected fields in China [ 33 ]. Very recently, some lignin biosynthesis pathway genes were reported to be related to S. sclerotiorum resistance in B. napus , such as BnF5H [ 5 ], BnCAD5 [ 34 ] and BnaC.CCR2 [ 4 ]. These findings indicate that increasing the lignin content in the stems of B. napus might be an effective strategy for controlling S. sclerotiorum .…”

The Characterization of the Phloem Protein 2 Gene Family Associated with Resistance to Sclerotinia sclerotiorum in Brassica napus

“…In recent years, an accumulating body of research has shown that some transcription factors and kinases are related to SD resistance signaling pathways, such as BnWRKY33 [ 41 , 42 ], BnWRKY70 [ 43 ], BnMPK3 [ 44 ], BnMPK4 [ 45 ], BnMPK6 [ 46 ] and AtGDSL1 [ 35 ]. Pathogenesis-related (PR) proteins, such as lipid transfer proteins [ 47 ], defensins [ 48 ] and thaumatin-like proteins [ 47 ], play positive roles in SD resistance, as well as some secondary metabolites synthesis, such as BnUGT74B1 [ 49 ] and lignin [ 50 ]. Researchers have also demonstrated that increasing the lignin content in the stem of B. napus is an important strategy to control Sclerotinia [ 51 ].…”