Mutation of MeMinD increased amyloplast size with a changed starch granule morphologenesis and structures in cassava storage roots

Abstract

Amyloplasts are the sites of starch synthesis and accumulation. Little is known about amyloplast division and its effects on the size, structure, and physicochemical properties of starch granules. In this study, we created mutants of plastid division-related gene MeMinD by CRISPR/Cas9 technology, leading to the disruption of normal division of amyloplasts in cassava storage roots. The memind mutants exhibited significantly enlarged amyloplasts with an increased number of starch granules, and broader range of granule sizes. The loss of MeMinD function led to transcriptional reprogramming of gene expressions related to starch-synthesizing enzymes, affecting the fine structure of starch. Starch in memind mutant storage roots showed a significantly decreased proportion of shorter amylopectin chains and an increased proportion of medium and long chains, which ultimately led to a significant increase in apparent amylose content (AAC) in memind mutants compared to that in WT. The changes in starch granule size and structure resulted in a significant increase in onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of the gelatinization process, extending the time to reach peak temperature. These data suggest that regulating amyloplast division affects starch accumulation in cassava, presenting an effective strategy for developing novel cassava starch.

Keywords: Amyloplast size; Cassava; MeMinD; Starch granule; Starch structure.