Abstract:

Gibberellins (GA) play an important role in regulating cotton fiber development. As the GA receptor, GID1 is an essential component of GA signaling pathway. To advance our understanding of GA’s functions in cotton development (especially fiber development), we cloned six cotton GID1 homologous genes (GhGID1-1–6, accession No. are FJ790125–FJ790130) by searching EST sequences, extending the flanking sequences by Y-shaped adaptor dependent extension (YADE) method and amplifying the full-length cDNA by 3'-RACE. Multiple sequence alignment indicated that the deduced GhGID1-1–6proteins 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 (G¹⁶⁹, G¹⁹⁶, and R²⁵¹) with the rice GID1 function were also conserved in cotton GID1s. In the phylogenetic tree of GhGID1-1–6 and other GID1 proteins with known function, GhGID1-1–6 were clustered with 3 Arabidopsis GID1 proteins, and distantly related to GID1s from rice and S. moellendorffii. Quantitative RT-PCR was employed to detect the expression levels of GhGID1-1–6 in various organs and tissues. The transcripts of GhGID1-1–6 could be detected in all the organs and tissues investigated (including roots, hypocotyls, leaves, petals, anthers, ovules and fibers), although with various levels. GhGID1-1 and GhGID1-2 expressed mainly in floral organs, while GhGID1-4 expressed preferentially in fiber and root. Exogenous GA added in medium led to alteration of gene expression level in the in vitro cultivated ovules, and the expressions of GhGID1-1 and GhGID1-2 were obviously inhibited by GA. These results suggested that GhGID1-1–6 might encode biologically functional GID1 homologues involved in GA signaling in cotton. To further clarify GID1 genes related to fiber development, we compared GhGID1s’ expression in developing ovule (from 6 to 18 days post anthesis, DPA) and the attached fibers by quantitative RT-PCR. GhGID1-1 was predominantly expressed in ovules, and its expression level reached the climax at 10 DPA, and kept the high level at 14 DPA and 18 DPA, while 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.

Key words: GID1, Cotton, Fiber development, Expression Specificity