Genome-wide identification and expression analysis of the GA2ox gene family in maize (Zea mays L.) under various abiotic stress conditions

GA 2-oxidases (GA2oxs) are a class of enzymes that inhibit the biosynthesis of bioactive GAs in plants. Although GA2oxs have clear roles in the development and defence responses in Arabidopsis, rice, and wheat, their potential effects on maize remain unclear. This study identified thirteen ZmGA2ox genes in maize and further characterized them using phylogenetic, gene structure, genomic locus, expression pattern analyses and GA content determination. Phylogenetic relationship analysis clearly divided the ZmGA2ox family into three groups—seven in C19-GA2ox class I, three in C19-GA2ox class II, and three in C20-GA2ox class. Evolutionary analysis suggested that ZmGA2ox1;1 and ZmGA2ox1;2, ZmGA2ox3;1 and ZmGA2ox3;2, and ZmGA2ox7;1 and ZmGA2ox7;2 are three pairs of segmental duplicated genes. Prediction of cis-regulatory elements in promoters suggested that ZmGA2ox genes were mainly associated with growth, development, hormones, and biotic/abiotic stress. Therefore, their spatial and temporal expression patterns and responses to various stress treatments were analysed on the basis of published RNA-seq data. Moreover, the changes of ZmGA2ox expression in leaves and roots of maize seedlings was detected under salt, alkali, dehydration, and cold stresses by qRT-PCR. The ZmGA2oxs exhibited obvious expression tendencies or characteristics in various organs under different abiotic stresses. The variations in the expression of three ZmGA2ox genes in the C20-GA2ox class in maize seedling roots showed significant regularity and a clear negative correlation with bioactive GA contents under cold and drought conditions, indicating that these three genes might exert key effects on the regulation of GA synthesis and the response to drought and cold stress. Taken together, this study is useful for further dissection of the effect of ZmGA2oxs on abiotic stress responses and might provide potential targets for the genetic improvement of maize.