Cloning and Characterization of a G Protein β Subunit Gene Responsive to Plant Hormones and Abiotic Stresses in Brassica napus

A full-length cDNA encoding a putative G protein beta subunit (G beta), designated as BnGB1, was isolated from Brassica napus. BnGB1 was predicted to encode a precursor protein of 378-amino acid residues. The expression of BnGB1 in different B. napus tissues and developmental stages was analyzed using real-time polymerase chain reaction. The results showed that BnGB1 expressed was high at the seventh day, the bolting stage, and fruiting stage. Moreover, BnGB1 was analyzed under four different plant hormones. All of the four tested hormones, abscisic acid (ABA), GA(3), brassinosteroid (BR), and indole-3-acetic acid (IAA), triggered an induction of BnGB1 at different hormone concentrations. The expression of BnGB1 was induced by low ABA concentrations, but high ABA concentrations inhibited the expression, which demonstrated that there might be an ABA-mediated feedback repression of the BnGB1 expression. BnGB1 was more prominently induced by high concentrations of GA(3) than by other plant hormones. The positive responses stimuli suggested that BnGB1 might be involved in signaling pathways for response to high concentrations of GA. However, the expression of BnGB1 did not significantly regulated by exogenous BR and IAA compared with the level regulated by ABA and GA(3). In addition, BnGB1 was responsive to different abiotic stresses and displayed differential expression patterns in B. napus. The BnGB1 was upregulated in salt and drought stress and downregulated in heat and cold stress. These results suggest that BnGB1 plays an important role in ABA and GA signal pathways and may also be involved in plant defense system against environmental stresses in B. napus.