Abstract:Starch synthases (SS) are key enzymes involved in starch biosynthesis pathways. Five isoforms of starch synthase have been identified and characterized functionally. To identify genes encoding new SS isoforms based on rich sorghum genome data, SbSSV, a new isoform of sorghum SSs have been identified and isolated by employing bioinformatics and molecular biology methods. The exon-intron structure and expression patterns of SbSSV have been analyzed. Results show that the ORF of SbSSV is 2 097 bp, with its exon numbers, lengths and intron distributions were consistent with those of its homologues in maize and rice. The predicted protein has conserved starch catalytic domain and glycosyltranferase domain, which are unique characteristics of glycogen synthases in bacteria and starch synthases in plants. A phylogenetic analysis of SSs in higher plants shows that SSV is closely related to the known SSIV. Therefore, we infer that the SbSSV encodes a new isoform of SSs in sorghum. qRT-PCR analysis indicates that SbSSV is mainly expressed in leaf with its expression induced by light and follows circadian rhythm. The results provide a theoretical basis for further revealing the mechanism of starch biosynthesis metabolism and improving yield and quality in crops.