Molecular cloning and expression analysis of a RGA-like gene responsive to plant hormones in Brassica napus

DELLA proteins are negative regulators of GA-induced growth. DELLA protein family is characterized by a DELLA domain essential for GA-dependent proteasomal degradation of DELLA repressors. A full-length cDNA encoding a putative DELLA protein with high sequence homology to Arabidopsis thaliana RGA (AtRGA), designated as BnRGA, was isolated from Brassica napus. The full-length cDNA of BnRGA contained a 1,740 bp open reading frame (ORF) encoding a precursor protein of 579 amino acid residues. Comparative and bio-informatics analyses revealed that BnRGA showed a high degree of homology with DELLA proteins and contained the DELLA domain, TVHYNP domain, VHIID domain and RVER domain. Using real-time PCR, the expression patterns of BnRGA and two our previously isolated genes, BnGID1a and BnSLY1 in B. napus, were analyzed by adding exogenous gibberellins acid-3 (GA(3)), GA biosynthetic inhibitor paclobutrazol (PAC) and abscisic acid (ABA). The results showed that the expression of BnGID1a and BnSLY1 was down-regulated after treated by GA(3) and induced by PAC and ABA. These results suggest that the expression of BnGID1a and BnSLY1 may be negatively regulated by the level of endogenous GA in B. napus. Moreover, BnRGA was not significantly regulated by GA(3), PAC and ABA in the low concentrations. These suggest that GA-GID1-SCF-DELLA complex may have a mechanism of self-regulation, thereby preserving the stability of the expression level of BnRGA in B. napus.