Evolutionary and expression analysis of starch synthase genes from Tartary buckwheat revealed the potential function of FtGBSSII-4 and FtGBSSII-5 in seed amylose biosynthesis

The starch synthase has been identified well as a core enzyme in the starch biosynthesis pathway in monocots. However, only a few starch synthase genes (SSs) are known in dicots. Tartary buckwheat (Fagopyrum tataricum Gaertn.) is one of the dicots-enriched starch in the seeds, but its starch synthesis pathway remains unclear. Here, 15 SS genes were identified in the Tartary buckwheat genome, including 5 granule-bound starch synthase (GBSS) and 10 soluble starch synthase (SSS) genes. Evolutionary analysis showed that all FtGBSSs belonged to GBSSII, and its isoforms were more abundant than other dicots due to the segmental duplication events. Expression pattern analysis showed two GBSS genes (FtGBSSII-4 and FtGBSSII-5) and three SSS genes (FtSSII-2, FtSSIII-1, and FtSSIV-2) were mainly expressed in seeds, indicating that they may be the dominant isoforms for the starch synthesis in Tartary buckwheat. Besides, 23 transcription factor genes out of 1073 were identified from 17 transcription factor families and highly expressed in seeds. Expression correlation analysis suggested that FtNF-YB2 may be the promising regulators for FtSSs. These results provide new insights and a theoretical basis for understanding starch synthesis and regulation in Tartary buckwheat and other dicots.