Functional And Digital Gene Expression Analyses Of GA Receptor CsGID1a In Cucumber

Gibberellins(GAs)are phytohormones with many roles in plant growth,including the regulation of seed germination,vegetative growth and reproductive development.However,little is known about the relationship between GA perception and fleshy fruit ontogeny,and particularly locule formation.In this study,cucumber(Cucumis sativus L.),a typical monoecious plant that produces fleshy fruit,was used as an experimental system to address this question.The main results are as follows:(1)CsGID1a and CsGID1b are two homologues of Arabidopsis.thaliana GID1 genes.An amino acid alignment revealed that CsGID1a and CsGID1b proteins have the conserved HSL motifs HGG and GXSXG.GA3 treatment caused a feedback regulation of CsGID1a and CsGIDlb.(2)Phylogenetic analysis revealed that CsGID1a and CsGID1b aligned with the GID1ac and GID1b groups,respectively.CsGID1a transcripts were expressed at far higher levels than those of CsGID1b in female flower buds and fruits,so we hypothesized that,of the two genes,CsGID1a is the more likely to play the predominant role in fruit development.This idea was supported by an RNAi experiment revealing that RNAi lines with significantly reduced CsGID1b transcript levels,in which the expression of CsGIDla was not altered compared with the control,showed normal height and fruit development.(3)The expression pattern of CsGID1a was found to be closely correlated with fruit locule formation by in situ hybridization and a promoter::GUS(?-glucuronidase)assay,and silencing CsGID1a in cucumber resulted in fruits with abnormal carpels and locules.The DGE analysis suggested that expression of genes related to auxin synthesis and transport,as well as the cell cycle,was altered in CsGID1a-RNAi fruits;a result that was supported by comparing the auxin content and cellular structures of the control and transgenic fruits.(4)Over-expression of CsGID1a in the Arabidopsis thaliana double mutant(gid1a gid1c)partial rescued of the semi-dwarfed phenotype and resulted in 'cucumber locule-like' fruits.