Cloning and Expression Profile of Gibberellin Insensitive Dwarf GID1 Homologous Genes from Cotton

Abstract

To advance the understanding of gibberellins (GA) functions in cotton ( Gossypium hisutum L.) development, especially fiber development, 6 cotton GID1 homologous genes, GhGID1-1 to GhGID1-6 (GenBank accession numbers FJ790125 to FJ790130), were cloned by searching expressed sequence tag (EST) sequences, extending the flanking sequences by Y-shaped adaptor dependent extension (YADE) method, and amplifying the full-length cDNA by 3′ rapid amplification of cDNA ends (RACE). Multiple sequence alignment indicated that the deduced GhGID1-1 to GhGID1-6 proteins shared high sequence identity with GID1s from other species and contained multiple binding sites with GA and DELLA protein, as well as HGG and GXSXG domains conserved in hormone-sensitive lipase (HSL) family. Three amino acid residuals (G 169, G 196, and R 251) related to rice ( Oryza sativa L.) GID1 were also conserved in cotton GID1s. In the phylogenetic tree of GhGID1s and GID1 proteins with known functions, GhGID1-1 to GhGID1-6 were clustered together with 3 Arabidopsis GID1 proteins, and distantly related to GID1s from rice and Selaginella moellendorffii. According to the results by quantitative reverse transcription polymerase chain reaction (RT-PCR), the transcripts of GhGID1-1 to GhGID1-6 were detected in roots, hypocotyls, leaves, petals, anthers, ovules, and fibers. GhGID1-1 and GhGID1-2 were expressed mainly in floral organs, and GhGID1-4 was expressed preferentially in fiber and root. Exogenous GA in medium resulted in alteration of gene expression level in the ovules cultivated in vitro, and the expression of GhGID1-1 and GhGID1-2 was obviously inhibited by GA. These results suggested that the 6 GhGID1 homologous genes might encode biologically functional GID1 homologues involved in GA signaling in cotton. GhGID1-1 was predominantly expressed in ovules; its expression level reached the climax at 10 d post anthesis (DPA) and maintained the high level at 14 DPA and 18 DPA. In fibers, GhGID1-4 was the main GID1 homologue expressed, and its highest-level expression occurred at 6 DPA and declined to a very low level at 14 DPA and 18 DPA. This result strongly suggested that these are relatively independent GA signaling systems in ovules and attached fibers.