Overexpression of chitinase <i>PbChia1</i> from <i>Plasmodiophora brassicae</i> improves broad-spectrum disease resistance of Arabidopsis

Chitinase plays an important role in plant resistance against chitin-containing pathogens through hydrolysis of chitin. Clubroot caused by <i>Plasmodiophora brassicae</i> is a major disease for cruciferous crops and vegetables worldwide. The cell wall of <i>P. brassicae</i> resting spores contains chitin. Chitinase is regarded as capable of improving plant resistance to fungal diseases. However, there has been no report about the function of chitinase in <i>P. brassicae</i>. Here, wheat germ agglutinin staining and commercial chitinase treatment demonstrated that chitin is a functional component in <i>P. brassicae</i>. In addition, Chitinase PbChia1 was identified by chitin pull-down assay combined with LC-MS/MS. PbChia1 was found to be a typical secreted chitinase, which could bind chitin with chitinase activity <i>in vitro</i>. PbChia1 could significantly decrease the resting spores of <i>P. brassicae</i> and therefore relieve the severity of clubroot symptom, with a biocontrol effect of 61.29%. Overexpression of <i>PbChia1</i> in <i>Arabidopsis thaliana</i> improved its resistance to <i>P. brassicae</i>, increased host survival rate and seed yield, enhanced PAMPs-triggered reactive oxygen species burst, MAPK activation and expression of immune-related genes. <i>PbChia1</i> transgenic plants also showed resistance to other pathogens, such as biotrophic bacterium <i>Pst</i> DC3000, necrotrophic fungi <i>Sclerotinia sclerotiorum</i> and <i>Rhizoctonia solani</i>. These findings indicate that chitinase <i>PbChia1</i> is a candidate gene that can confer broad-spectrum disease resistance in breeding.