The Arabidopsis RGA Gene Encodes a Transcriptional Regulator Repressing the Gibberellin Signal Transduction Pathway

Abstract

The recessive rga mutation is able to partially suppress phenotypic defects of the Arabidopsis gibberellin (GA) biosynthetic mutant ga1-3 . Defects in stem elongation, flowering time, and leaf abaxial trichome initiation are suppressed by rga . This indicates that RGA is a negative regulator of the GA signal transduction pathway. We have identified 10 additional alleles of rga from a fast-neutron mutagenized ga1-3 population and used them to isolate the RGA gene by genomic subtraction. Our data suggest that RGA may be functioning as a transcriptional regulator. RGA was found to be a member of the VHIID regulatory family, which includes the radial root organizing gene SCARECROW and another GA signal transduction repressor, GAI . RGA and GAI proteins share a high degree of homology, but their N termini are more divergent. The presence of several structural features, including homopolymeric serine and threonine residues, a putative nuclear localization signal, leucine heptad repeats, and an LXXLL motif, indicates that the RGA protein may be a transcriptional regulator that represses the GA response. In support of the putative nuclear localization signal, we demonstrated that a transiently expressed green fluorescent protein-RGA fusion protein is localized to the nucleus in onion epidermal cells. Because the rga mutation abolished the high level of expression of the GA biosynthetic gene GA4 in the ga1-3 mutant background, we conclude that RGA may also play a role in controlling GA biosynthesis.

Bioinformatic analyses of GRAS genes in Betula kirghisorum based on transcriptome data

“…Therefore, subcellular localization of proteins is essential for studying protein function. In the plant GRAS gene family, fusion of green fluorescent proteins with GRAS proteins, such as MtSymSCL1 (Kim andNam, 2013), NtGRAS1 (Czikkel andMaxwell, 2007), AtRGA (Silverstone et al, 1998), AtRGL1 (Wen and Chang, 2002), AtSCL14 (Fode et al, 2008), OsCIGR1 and OsCIGR2 (Day et al, 2003), OsGAI (SLR1) (Ogawa et al, 2000), and LiSCL (Morohashi, et al, 2003) generated green fluorescence in the nucleus, consistent with the functional characteristics of transcription factors. The predicted subcellular location of BkGRAS1, 2, 5, 7, 8, 9, 13, and 17 proteins was the nucleus, which is consistent with the known characteristics of transcription factors.…”

“…GRAS proteins play important roles in plant growth and development, and help plants to resist stress occurring in response to temperatures, drought, salt, and abiotic stress. The name of the gene family GRAS was designed from the first three functionally characterized members (GAI, RGA, SCR) ( Di Laurenzio et al, 1996;Peng et al, 1997;Silverstone et al, 1998;Pysh et al, 1999). GRAS proteins have variable N-terminal domains and conserved C-terminal domains.…”

MOLECULAR BASIS OF THE DWARFISM CHARACTER IN CULTIVATED PLANTS. II. DELLA-PROTEINS: STRUCTURE AND FUNCTIONS (review)

“…Double mutations GAI and RGA restored the height of ga1-3 plants to the wild-type level. Mutations in 3-5 genes of DELLA proteins converted short ga1-3 plants into giants [7,20,22,24]. (23), B -induction of GA-independent growth in dwarf ga1-3 mutant with loos of repressing function of DELLA proteins [7,22,24]; WT -wild type; gai-t6, rga-t2, rgl1-1, rgl2-1, rgl3-3 -mutations in DELLA proteins.…”

“…DELLA family proteins are nuclear-localized [10,25,26] and containing nuclear localization signal [10,20]. DELLA means a characteristic conserved sequence of Asp-Glu-Leu-Leu-Ala ((D-E-L-L-A) at the N-end of the polypeptide.…”

“…Mutations and deletions in DELLA and VHYNP motifs result in a dominant GA-insensitive dwarfing phenotype in which the plant height is not restored by exogenous GA [15,30,32]. For example, the dwarfing gai mutants in Arabidopsis and slr1-d1, slr1-d2, slr1-d3 in rice with a lesion in DEL-LA/TVHYNP domain are unable to binding to GID1 [19,20]. Interestingly, two SLRL genes (SLR1-like1, SLR1-like2) encoding proteins lacking DELLA domain are found in rice.…”