Cloning and expression analysis of Rsk in Brassica napus induced by Sclerotinia sclerotiorum

Based on the significant differences in the resistance to Sclerotinia sclerotiorum between two Brassica napus cultivars, ZhongR888 and Zhongyou821, near isogenic lines (NILs) were established. The resistance differences between Zhongyou821 and BC5 progeny (the fifth generation from a cross between Zhongyou821 and ZhongR888 with Zhongyou821 as successive backcross parent) was displayed by cDNA-AFLP and differential transcripts-derived fragments (TDFs). The full-length cDNA of 1,707 bp with 1,323 bp open reading frame (ORF, open box), named Rsk was identified by RT-RACE from the resistance related fragment 40-2 in Zhongyou821. It encoded a protein of 440 amino acid residues, which contained a putative extracellular domain, a transmembrane domain, and an intracellular domain. Analysis of the deduced amino acid sequence of Rsk revealed that it had high homology to Arabidopsis thaliana kinase involved in protein binding, and had a conserved region of LRR-RI, indicating it might be a member of leucine-rich repeats, ribonuclease inhibitor-like subfamily. DNA sequences of 1,685 bp and 1,703 bp without an intron were also identified from Zhongyou821 and BC5, respectively. Expression analysis showed that Rsk might play a role in disease resistance pathways.