Mutation in the GA3ox gene governs short-internode characteristic in a korean cucumber inbred line

Here, we identified a new natural mutant, si-2, from a Korean cucumber inbred line. The genes responsible for dwarf (DW) and/or short internode (SI) in cucurbits were selected and used to identify the gene(s) controlling the si-2 phenotype. We evaluated the transcript levels of the candidate genes between wild type (WT) and si-2 mutant and identified sequence polymorphism from the differentially expressed genes between the WT and si-2 mutants. Finally, we identified that CsGy7G019320 encodes GA3ox (gibberellin 3-beta-dioxygenase 1-like protein) with an SNP (single nucleotide polymorphism; A LOZENGE G) in an intron and a 20 bp deletion in the si-2 mutant. This fact strongly speculates that the GA3ox-mediated gibberellic acid (GA) signaling pathway could be involved in the si-2 mutant. It is well known that GAs have a significant impact on plant growth and development. In the si-2 mutant, a 20 bp deletion in the promoter may abolished the transcript levels of CsGy7G019320. Promoter analysis indicated that the 20 bp deleted promoter sequence of CsGy7G019320 may be considered as the AT-hook protein binding site. Although the involvement of the genes encoding GA3ox and AT-hook protein in GA signaling has been well identified, a 20 bp deletion in the promoter sequence of GA3ox in cucumber has not been revealed in other studies. Our data suggests that a mutation in the promoter sequence of CsGy7G019320 caused the si-2 mutant phenotype by suppression of GA3ox expression, possibly leading to decreased GA content in cucumber.