Overexpression of ZmSUS1 increased drought resistance of maize (Zea mays L.) by regulating sucrose metabolism and soluble sugar content
Sucrose synthase (SUS), a key enzyme of sugar metabolism, plays an important role in the regulation of carbon partitioning in plant, and affects important agronomic traits and abiotic responses to adversity. However, the function of ZmSUS1 in plant drought tolerance is still unknown. In this study, the expression patterns of ZmSUS1 in different tissues and under drought stress were analyzed in maize (Zea mays L.). It was found that ZmSUS1 was highly expressed during kernel development but also in leaves and roots of maize, and ZmSUS1 was induced by drought stress. Homozygous transgenic maize lines of ZmSUS1 overexpressing increased the content and activity of SUS under drought stress and exhibited higher relative water content, proline and abscisic acid content in leaves. Specifically, the net photosynthetic rate and the soluble sugar contents including sucrose?glucose?fructose?UDP-glucose and ADP-glucose in transgenic plants was significantly improved after drought stress. RNA-seq analysis showed that overexpressing of ZmSUS1 mainly affected the expression level of carbon metabolism-related genes, especially the expression level of  sucrose metabolism-related genes including ZmSUS?ZmSPS and ZmINV were significantly up-regulated in transgenic maize. Overall, these results suggested that ZmSUS1 improved drought tolerance by regulating sucrose metabolism and increasing soluble sugar content, and endowing transgenic maize with higher relative water content and photosynthesis levels, which can be served as a new gene candidate for cultivating drought resistant maize varieties. Overall design: A transgenic strain (T) was selected with its non-transgenic negative control (CK) for RNA-seq analysis, with three biological replicates selected each. RNA is extracted from leaf after 5 days of drought. RNA sequencing