Isolation and Molecular Characterization of Defense-Inducible PR2 Gene and its Promoter from Brassica juncea.

Abstract

Pathogenesis-related (PR) proteins play key roles in plant disease resistance. Here, we isolated and characterized pathogenesis-related PR2 gene encoding β-1,3-glucanase from Brassica juncea and named it BjPR2 (GenBank accession number DQ359125). The amino acid sequence of BjPR2 showed ~99 % similarity with β-1,3-glucanase of Brassica rapa, B. napus, and B. oleracea. BjPR2 transcription was rapidly increased after Alternaria brassicae infection, salicylic acid application, and wounding, but the induction was delayed in response to jasmonic acid. To investigate the transcriptional regulation of BjPR2 gene, its promoter was isolated. In silico analysis of BjPR2 promoter showed cis-regulatory elements upstream of TATA and CAAT boxes responsive to defense, hormones, wounding, and plant developmental stage. Homozygous Arabidopsis thaliana lines were developed with plasmid construct having β-glucuronidase (GUS) reporter gene driven by BjPR2 promoter. The analysis of GUS protein in Arabidopsis lines showed that BjPR2 promoter drived distinct pattern of pathogen inducible expression after fungal infection (Alternaria brassicae, Erysiphe orontii), phytohormones, and wounding. It also showed age dependent and organ specific expressions. BjPR2 promoter drove strong GUS activity in Arabidopsis seedlings and showed organ specific expression at the later growth stages (lateral organ junctions, leaf serrate, base of siliques, and receptacle). Due to stress-inducible and tissue specific nature, the BjPR2 promoter can serve as a potential candidate in genetic engineering. Additional key words: Alternaria brassicae, Arabidopsis thaliana, β-glucuronidase, Indian mustard, jasmonic acid, phylogenetic tree, salicylic acid, transgenic plant.