Comprehensive Analysis of Cucumber Gibberellin Oxidase Family Genes and Functional Characterization of CsGA20ox1 in Root Development in Arabidopsis

Abstract

Cucumber (<i>Cucumis sativus</i> L.) is an important vegetable crop worldwide and gibberellins (GAs) play important roles in the regulation of cucumber developmental and growth processes. GA oxidases (GAoxs), which are encoded by different gene subfamilies, are particularly important in regulating bioactive GA levels by catalyzing the later steps in the biosynthetic pathway. Although GAoxs are critical enzymes in GA synthesis pathway, little is known about <i>GAox</i> genes in cucumber, in particular about their evolutionary relationships, expression profiles and biological function. In this study, we identified 17 <i>GAox</i> genes in cucumber genome and classified them into five subfamilies based on a phylogenetic tree, gene structures, and conserved motifs. Synteny analysis indicated that the tandem duplication or segmental duplication events played a minor role in the expansion of cucumber <i>GA2ox</i>, <i>GA3ox</i> and <i>GA7ox</i> gene families. Comparative syntenic analysis combined with phylogenetic analysis provided deep insight into the phylogenetic relationships of <i>CsGAox</i> genes and suggested that protein homology CsGAox are closer to AtGAox than OsGAox. In addition, candidate transcription factors BBR/BPC (BARLEY B RECOMBINANT/BASIC PENTACYSTEINE) and GRAS (GIBBERELLIC ACID-INSENSITIVE, REPRESSOR of GAI, and SCARECROW) which may directly bind promoters of <i>CsGAox</i> genes were predicted. Expression profiles derived from transcriptome data indicated that some <i>CsGAox</i> genes, especially <i>CsGA20ox1</i>, are highly expressed in seedling roots and were down-regulated under GA₃ treatment. Ectopic over-expression of <i>CsGA20ox1</i> in <i>Arabidopsis</i> significantly increased primary root length and lateral root number. Taken together, comprehensive analysis of <i>CsGAoxs</i> would provide a basis for understanding the evolution and function of the <i>CsGAox</i> family.