Two Osgasr Genes, Rice Gast Homologue Genes That Are Abundant In Proliferating Tissues, Show Different Expression Patterns In Developing Panicles

Two different types of genes for rice GA-stimulated transcript (GAST) homologue genes, Oryza sativa GA-stimulated transcript-related gene 1 (OsGASR1) and gene 2 (OsGASR2), were found. Both OsGASR proteins contain a cysteine-rich domain highly conserved among GAST family proteins in their C-terminal regions. Gibberellin A(3) (GA(3)) stimulated expression of both OsGASRs in the wild-type Nipponbare and GA(3) synthesis-deficient mutant. Expression of both OsGASRs apparently increased when cell proliferation entered the logarithmic phase, and rapidly reduced when cell proliferation was temporarily halted. RTPCR analysis indicated different expression patterns of these genes in developing panicles. OsGASR1 was limitedly but strongly expressed in florets while OsGASR2 was expressed in both florets and branches. In situ hybridization showed that they were strongly expressed in the root apical meristem (RAM) and shoot apical meristem (SAM), but little signals were detected in mature leaves. Transient expression of OsGASR-GFP fusion proteins in onion epidermal cells revealed that both OsGASR proteins localized to the apoplasm or cell wall. These results suggest that OsGASR1 and OsGASR2 were involved in cell division and might play diverse roles in differentation of panicles.