Plasmodiophora brassicae Infection Modulates Expansin Genes of Brassica rapa ssp. pekinensis

Abstract

Clubroot is a soil-borne disease of cruciferous crops, including Brassica rapa ssp. pekinensis, and causes substantial yield losses. In an attempt to develop clubroot-resistant B. rapa cultivars, we investigated the role of a root-abundant expansin-like B1 (EXLB1) during Plasmodiophora brassicae inoculation. The histochemical analyses of infected transgenic reporter lines showed a role for BrEXLB1 in disease response as early as 3 dpi. The transgenic overexpression of EXLB1 in B. rapa conferred disease-sensitive phenotypes and was comparable to non-transgenic controls at 30 dpi. In contrast, the heterogeneous population of antisense BrEXLB1-overexpressing lines conferred disease resistance against highly pathogenic P. brassicae race 2 inoculations under greenhouse conditions. Additionally, we profiled the relative expression of 32 other BrEXPs in wild-type seedlings, sampled on different days (1–10) after inoculation using qRT-PCR. The results indicate that the expression pattern of most BrEXP genes was significantly altered during different infection times, suggesting their participation in clubroot responses. In particular, the expressions of EXPA20, EXPA21, and EXPA34 were consistently downregulated, while the expression of EXPA5 was upregulated (log2FC ≥ 2) compared to controls. Altogether, our study showed that BrEXPs participate in clubroot disease response, and their genetic manipulation is likely to provide clubroot disease resistance.