Genome-wide identification of the GAox gene family and functional characterization of PbGA3ox4 during stone cell formation in Chinese white pear

Gibberellin (GA) is one of the most important phytohormones that regulates multiple developmental processes in plants, including fruit quality. Stone cell of pear is the key determinant negatively influencing fruit quality, because of the lignified cell walls. The effect of GA in pear stone cell formation is still unknown and the distribution of GA oxidases (GAoxs) genes in the pear (Pyrus bretschneideri) genome remains uncharacterized. In this study, stone cells and endogenous GA3 were found to be co-localized in lignified cells by immunofluorescence localization analysis. Then, a comprehensive bioinformatics analysis of the GAox gene family in the pear genome was performed. Genome-wide identification of the PbGAoxs revealed 27 genes encoding PbGAox proteins, which could be divided into four subfamilies (GA20ox, C19-GA2ox, GA3ox, and C20-GA2ox). Cis-element analysis indicated that PbGAox genes might be involved in plant hormones and light signaling. Evolution and sequence alignment analysis indicated that PbGA3ox4 was responsible for the biosynthesis of bioactive GA3. The biological function of PbGA3ox4 in promoting GA3 biosynthesis and cell lignification has been illustrated by overexpression in pear fleshcalli and Arabidopsis. Collectively, this study laid a foundation for the functional analysis of the pear GAox family and provided valuable genetic resources for the improvement of pear fruit quality.