Isolation and characterization of systemic acquired resistance marker gene PR1 and its promoter from Brassica juncea

Systemic acquired resistance (SAR) is an inducible defense response in plants that provides enhanced resistance against a variety of pathogens. In this regard, SAR marker gene PR1 (pathogenesis-related gene 1) was isolated from Brassica juncea and was named as BjPR1. The amino acid sequence of BjPR1 protein showed 99, 92, and 78% similarity with known PR1 proteins of Brassica rapa, Brassica napus, and Arabidopsis thaliana, respectively. Quantitative real-time PCR (qRT-PCR) analysis showed increased expression of BjPR1 gene both in local (infected) and distal (non-infected) leaves of B. juncea after Alternaria brassicae infection, whereas mechanical wounding showed expression only in local (wounded) leaves but not in distal (unwounded) leaves. Moreover, BjPR1 gene was strongly induced by salicylic acid (SA), whereas no such induction was observed following jasmonic acid (JA) or abscisic acid (ABA) treatments. To further elucidate gene regulation pattern of BjPR1, 2 kb promoter region of BjPR1 was isolated and subjected to in silico analysis which identified many potential cis-regulatory elements associated with plant defense as well as signaling pathways. The transient GUS expression analysis showed strong expression of GUS gene driven by BjPR1 promoter after SA treatment, while as ABA and JA downregulates GUS gene expression compared to control. In addition, BjPR1 promoter was significantly induced by wounding at local tissues. Hence, these results highlight the multiple role of BjPR1 gene in response to biotic and abiotic stresses. In addition, the present study also reported BjPR1 promoter as stress-specific inducible promoter that can be ideal candidate for controlling the expression of biotic stress response genes in transgenic plants.