Wheat gibberellin oxidase genes and their functions in regulating tillering

Abstract

Multiple genetic factors control tillering, a key agronomy trait for wheat (<i>Triticum aestivum</i> L.) yield. Previously, we reported a <i>dwarf-monoculm</i> mutant (<i>dmc</i>) derived from wheat cultivar Guomai 301, and found that the contents of gibberellic acid 3 (GA₃) in the tiller primordia of <i>dmc</i> were significantly higher. Transcriptome analysis indicated that some wheat gibberellin oxidase (<i>TaGAox</i>) genes <i>TaGA20ox-A2</i>, <i>TaGA20ox-B2</i>, <i>TaGA3ox-A2</i>, <i>TaGA20ox-A4</i>, <i>TaGA2ox-A10</i> and <i>TaGA2ox-B10</i> were differentially expressed in <i>dmc</i>. Therefore, this study systematically analyzed the roles of gibberellin oxidase genes during wheat tillering. A total of 63 <i>TaGAox</i> genes were identified by whole genome analysis. The TaGAoxs were clustered to four subfamilies, GA20oxs, GA2oxs, GA3oxs and GA7oxs, including seven subgroups based on their protein structures. The promoter regions of <i>TaGAox</i> genes contain a large number of <i>cis</i>-acting elements closely related to hormone, plant growth and development, light, and abiotic stress responses. Segmental duplication events played a major role in <i>TaGAoxs</i> expansion. Compared to <i>Arabidopsis</i>, the gene collinearity degrees of the <i>GAoxs</i> were significantly higher among wheat, rice and maize. <i>TaGAox</i> genes showed tissue-specific expression patterns. The expressions of <i>TaGAox</i> genes (<i>TaGA20ox-B2</i>, <i>TaGA7ox-A1</i>, <i>TaGA2ox10</i> and <i>TaGA3ox-A2</i>) were significantly affected by exogenous GA₃ applications, which also significantly promoted tillering of Guomai 301, but didn't promote <i>dmc</i>. <i>TaGA7ox-A1</i> overexpression transgenic wheat lines were obtained by <i>Agrobacterium</i> mediated transformation. Genomic PCR and first-generation sequencing demonstrated that the gene was integrated into the wheat genome. Association analysis of <i>TaGA7ox-A1</i> expression level and tiller number per plant demonstrated that the tillering capacities of some <i>TaGA7ox-A1</i> transgenic lines were increased. These data demonstrated that some <i>TaGAoxs</i> as well as GA signaling were involved in regulating wheat tillering, but the GA signaling pathway was disturbed in <i>dmc</i>. This study provided valuable clues for functional characterization of <i>GAox</i> genes in wheat.