Starch accumulation and starch related genes expression in novel inter-specific inbred squash line and their parents during fruit development

Dry matter and starch composition during squash fruit development were observed in Cucurbita maxima (Indian squash), Cucurbita moschata (Chinese squash) and their inter-specific inbred line, namely Maxchata. Five genes associated with starch biosynthesis were isolated and analyzed for their expression patterns using quantitative RT-PCR to elucidate the molecular mechanism of starch biosynthesis in squash fruit. The two squash species and their inter-specific inbred line exhibited difference in starch composition and corresponding regulatory mechanisms. C. moschata had the lowest total starch content that can be correlated with the lower transcript levels of AGPaseL gene as compared to the other squashes. Starch content in C. maxima and Maxchata was not significantly different in mature fruit. The higher expression of the AGPaseL genes resulted in more starch accumulation in these squashes. However, AGPaseL gene in Maxchata was highly expressed at early fruit development that led to rapid increase in starch accumulation at early stage of fruit development. Likewise, high GBSSI gene expression in C. maxima and Maxchata triggered more amylose accumulation. In contrast, SSII, SBEII, and ISAI genes, responsible for amylopectin synthesis, were expressed late during fruit development with no significant difference in their transcript levels.

► Different regulation of starch biosynthesis was found between Cucurbita species.
► AGPaseL transcript levels were associated with total starch accumulation.
► Cucurbita moschata had lowest starch content as expected in low expression of AGPaseL gene.
► GBSSI gene expression related with high amylose content in Cucurbita maxima and Maxchata.
► Maxchata seems to be an interesting source for the early harvested squash fruit.