CRISPR/Cas9 mediated knockout of MeSSI enhances resistant starch content without compromising yield in cassava

Enhancing resistant starch (RS) content in cassava is vital for developing nutritionally improved, functional food crops. In this study, targeted mutagenesis of the MeSSI gene via CRISPR/Cas9 was conducted to investigate its role in starch biosynthesis and RS accumulation. MeSSI knockout lines exhibited a 6.74-fold increase in RS content and a 16.42% elevation in amylose levels compared to the wild-type, without compromising total starch content or root yield. Starch structural analysis revealed an increased number of smaller granules per amyloplast and a shift in amylopectin chain-length distribution, characterized by reduced short chains (DP 6-12) and enrichment of intermediate and long chains, resulting in a lower branching degree. These modifications were associated with enhanced thermal stability and altered pasting behavior. Transcriptomic profiling indicated compensatory upregulation of AGPase subunits, and glycolytic genes, suggesting a reprogramming of carbon metabolism to sustain starch accumulation. This work identifies MeSSI as a key determinant of amylopectin fine structure and RS formation, providing a precise genome-editing strategy to improve the nutritional profile of cassava.