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GASA, a gibberellin-regulated gene family from Arabidopsis thaliana related to the tomato GAST1 gene.

A multiple gene family of at least four members, related to a GA-stimulated transcript (GAST1) from tomato, was characterized in Arabidopsis thaliana by analysing four related cDNAs, named GASA1 to GASA4. The corresponding peptides display comparable structural features: (1) a putative signal peptide of 18 to 23 residues; (2) a highly divergent hydrophilic region of about 22 amino acids; (3) a conservative 60 amino acid C-terminal domain containing 12 cysteines. This organization has also bean shown in two related peptides from tomato, GAST1 found in shoots and RSI-1 found in early lateral roots. Southern blot hybridization patterns showed single-copy genes for all four members of the GASA family. Accumulation of the various transcripts, monitored by northern blot hybridization, indicated that the various genes are expressed differentially in plant organs: Specific mRNAs were mostly detected in flower buds and immature siliques in the case of GASA1, in siliques and dry seeds in the case of GASA2 and 3, and in growing roots and flower buds in the case of GASA4. At least two of the GASA genes are activated in GA-deficient mutant ga5, as early as 4 to 8 h after spraying with 50 microM GA3. The complex patterns of expression and regulation of the various genes suggest that the related peptides are involved in a developmental regulation process in Arabidopsis.

Amino Acid Sequence↗

Analysis of the gibberellin-responsive promoter of a cathepsin B-like gene from wheat.

A wheat gene (A121) encoding a protein with sequence similarity to mammalian cathepsin B is regulated by gibberellic acid (GA) in aleurone layers of germinating grains. To analyse the mechanism of A121 regulation, its promoter was fused to the beta-glucuronidase reporter gene (GUS) and introduced by micro-projectile bombardment into aleurone layers of oat. With 2.3 kb of promoter sequence, the GUS expression was enhanced by GA treatment. This effect was reversed by abscisic acid (ABA). This result showed for A121, like the alpha-amylase genes, that the regulation by GA and ABA was at the level of transcription. The GA responsiveness of the promoter was retained with as little as 276 bp of promoter sequence. Sequence comparison with a GA responsive promoter of an alpha-amylase gene identified the conserved element GCAACGGCAACGATGG which is required intact for full expression of both promoters. However, there was no identifiable similarity in the cathepsin-like promoter with the GA-responsive element of alpha-amylase promoters with the consensus sequence TAACAAA, suggesting that GA affects more than one mechanism of transcriptional control.

Abscisic Acid↗