Characterization of a shoot‐specific, GA₃‐ and ABA‐Regulated gene from tomato

A tomato (Lycopersicon esculentum) gene (GAST1) that encodes an RNA whose abundance increases > 20‐fold in shoots of the GA‐deficient gib 1 mutant following spraying with GA₃ has been characterized. An increase in GAST1 RNA levels is detectable 2 h after treatment and levels continue to increase for at least an additional 10 h. Between 12 and 24 h following treatment, the amount of GAST1 RNA begins to decline and at 48 h the level is nearly equivalent to that of water‐treated control plants. Nuclear runoff analysis indicates that 8 h after treatment with GA₃, transcription of the GAST1 gene has increased only threefold, suggesting that GA acts both transcriptionally and post‐transcriptionally. ABA partially inhibits the GA‐mediated increase in GAST1 RNA abundance while ethephon, kinetin, and 2, 4‐D have little effect. GAST1 RNA is detectable in untreated leaves, stems, petioles and flowers, but not in roots. The GAST1 gene encodes a 0.7 kb transcript. The sequence of the GAST1 cDNA and genomic clones indicates that the gene is interrupted by three introns and potentially encodes a 112 amino acid protein of unknown function.