Overexpression of Cinnamoyl-CoA Reductase 2 in Brassica napus Increases Resistance to Sclerotinia sclerotiorum by Affecting Lignin Biosynthesis

Abstract

<i>Sclerotinia sclerotiorum</i> causes severe yield and economic losses for many crop and vegetable species, especially <i>Brassica napus</i>. To date, no immune <i>B. napus</i> germplasm has been identified, giving rise to a major challenge in the breeding of <i>Sclerotinia</i> resistance. In the present study, we found that, compared with a <i>Sclerotinia</i>-susceptible line (J902), a <i>Sclerotinia</i>-resistant line (J964) exhibited better xylem development and a higher lignin content in the stems, which may limit the invasion and spread of <i>S. sclerotiorum</i> during the early infection period. In addition, genes involved in lignin biosynthesis were induced under <i>S. sclerotiorum</i> infection in both lines, indicating that lignin was deposited proactively in infected tissues. We then overexpressed <i>BnaC.CCR2.b</i>, which encodes the first rate-limiting enzyme (cinnamoyl-CoA reductase) that catalyzes the reaction of lignin-specific pathways, and found that overexpression of <i>BnaC.CCR2.b</i> increased the lignin content in the stems of <i>B. napus</i> by 2.28-2.76% under normal growth conditions. We further evaluated the <i>Sclerotinia</i> resistance of <i>BnaC.CCR2.b</i> overexpression lines at the flower-termination stage and found that the disease lesions on the stems of plants in the T₂ and T₃ generations decreased by 12.2-33.7% and 32.5-37.3% compared to non-transgenic control plants, respectively, at 7days post-inoculation (dpi). The above results indicate that overexpression of <i>BnaC.CCR2.b</i> leads to an increase in lignin content in the stems, which subsequently leads to increased resistance to <i>S. sclerotiorum</i>. Our findings demonstrate that increasing the lignin content in the stems of <i>B. napus</i> is an important strategy for controlling <i>Sclerotinia</i>.