Isolation and Expression Analysis of Sucrose Synthase Gene (ScSuSy4) from Sugarcane

Sucrose synthase is one of the key enzymes involved in sucrose metabolism. In order to increase the sucrose content at the molecular level, it is very necessary to understand the biological function of sucrose synthase gene in sugarcane. In this study, homology cloning and rapid amplification of cDNA ends technology were used to obtain the 2898 bp full-length cDNA of ScSuSy4 in sugarcane, which contains an opening reading frame of 2430 bp (GenBank: KM598653). This gene encodes a protein of 809 amino acids with a theoretical molecular weight of 92.31 kDa and an isoelectric point of 6.30. The amino acid sequence homologies between ScSuSy4 and SbSus4, ZmSus3 and OsSus4 from Group II were 99.5, 98.3, and 97.2 %, respectively. Expression analysis showed that at the elongation stage of low-sugar and medium-sugar sugarcane species, the expression level of ScSuSy4 in immature stems was higher than that in mature leaves, whereas in all three high-sugar species, ScSuSy4 gene expression levels were higher in mature leaves than that in immature stems. At the early stage of sucrose accumulation, expression levels of ScSuSy4 in all species were lower in immature stems than that in mature leaves. At different stages of the same species, regardless in immature stems or in mature leaves, ScSuSy4 gene expression reached the highest level at the elongation stage, dropped to the lowest level at early stage of sucrose accumulation, and increased again at late stage of sucrose accumulation. It is putative that ScSuSy4 gene might be involved in the regulation of sucrose distribution via different functions at various stages. This study provides a foundation for further dissection of the biological function of this gene.