Role of BjuA03.BNT1  in enhancing clubroot resistance in resynthesized Brassica juncea  L.

Abstract

In recent years, clubroot disease has emerged as a significant impediment to rapeseed production. Breeding new varieties resistant to clubroot is the most effective method for disease management. However, the pool of clubroot-resistant germplasm of rapeseed remains notably limited. In order to address this challenge, we synthesized the clubroot-resistant mustard, CT19, via remote hybridization, and subsequently an F2 segregating population was created by intercrossing CT19 with a clubroot-susceptible germplasm CS15. A major-effect QTL qCRa3-1 on chromosome A03 was identified through QTL scanning, demonstrating a substantial association with clubroot resistance. Transcriptome analyses of CT19 and CS15 revealed that the mechanisms conferring resistance to Plasmodiophora brassica likely involved the regulation of flavonoid metabolism, fatty acid metabolism, and sulfur metabolism. By combining the results from transcriptome analyses, QTL mapping and gene sequencing, a candidate gene BjuA03.BNT1, encoding TIR-NBS-LRR protein, was obtained within the region of qCRa3-1. Intriguingly, an insertion of a base T in the CDS of BjuA03.BNT1 in CT19 was discovered, which caused an alteration within the conserved domain TIR. Overexpression of BjuA03.BNT1 of CT19 notably enhanced the resistance to clubroot while overexpression of BjuA03.BNT1 of CS15 augmented susceptibility to the disease in Arabidopsis. Our investigations revealed that BjuA03.BNT1 regulated the resistance to clubroot by modulating fatty acid synthesis and the structure of cell wall. The one base insertion in the CDS of BjuA03.BNT1 serves as a pivotal determinant in conferring resistance to clubroot. These findings bear significant implications for molecular breeding aimed at enhancing clubroot resistance in rapeseed.