Brassica rapa expansin-like B1 gene (BrEXLB1) regulate growth and development in transgenic Arabidopsis and elicits response to abiotic stresses

The functional role of expansin-like A and B family members remains unclear in plants. In this study, we investigate the functional role of Brassica rapa expansin-like B1 (BrEXLB1) by overexpressing BrEXLB1 sense, antisense and BrEXLB1 specific promoter: GUS in Arabidopsis. The overexpressors of sense BrEXLB1, antisense BrEXLB1 showed variable and unstable pleiotropic effects on leaf growth. Interestingly, overexpressors of sense BrEXLB1 enhances plant height than antisense overexpressors and wild types. GUS reporter-aided analysis of BrEXLB1 promoter showed their activity prominently in seeds, roots and carpels. This is further confirmed by relative quantification of BrEXLB1 among various tissue samples of B. rapa by semi-quantitative Reverse transcription-polymerase chain reaction assay (RT-PCR). We found that BrEXLB1 promoter has several cis-acting elements including light-responsive, phytohormone-responsive, environmental/stress-responsive and tissue-specific elements in promoter sequences. Hence, we analysed the promoter activity of BrEXLB1 by GUS reporter-aided approach, in which stress, phytohormones and other factors regulated changes in GUS transcripts were measured using quantitative RT-PCR. This study suggests that promoter activity is inducible to exogenous application of phytohormones such as indole-3-acetic acid, jasmonic acid, and other factors such as white light and drought stress. These results suggest that BrEXLB1 under its specific promoters may participate in regulation of leaf, plant growth and responds to hormone availability, light quality, dark periods, developmental stages, and drought conditions.