Genome-wide identification and expression analysis of chitinase gene family in Brassica rapa reveals its role in clubroot resistance

Abstract Chitinases, a category of pathogenesis-related proteins, are responsible for catalyzing the hydrolysis of chitin into the N -acetyl- d -glucosamine. Therefore, chitinases are believed to function as a guardian against chitin-containing pathogens. Here, we examined the role of the Brassica rapa chitinase family genes in clubroot disease. A total of 33 chitinase genes were identified and grouped into five classes based on their conserved domain. They were distributed unevenly across eight chromosomes in B . rapa , and 31 of them contained few introns (≤2). In addition, the expression of these genes was organ-specific, and 14 genes were expressed differentially in response to Plasmodiophora brassicae challenge of clubroot-susceptible (CS NIL) and resistant (CR NIL) lines. Furthermore, reduced pathogen DNA content and clubroot symptoms were observed in the CS NILs after their treatment with chitin oligosaccharides 24 h prior to inoculation with P. brassicae . The findings indicate that chitinases play a crucial role in pathogen resistance of the host plants. The results offer an insight into the role of chitinase in B. rapa–P. brassicae interaction.