Efficient promoter editing of the SBEIIb gene enables fine-tuning of the resistant starch content in rice

Rice, a staple in diets, undergoes digestion post-consumption, often triggering a swift surge in blood sugar among diabetics, intensifying their health burden. Notably, resistant starch (RS) emerges as a potent ally in fostering satiety and mitigating metabolic syndrome in diabetes. The SBEIIb gene, a key orchestrator of starch branching enzymes, plays a pivotal role in starch synthesis, and its genetic alteration can dramatically boost RS content in rice. Cultivating RS-rich functional germplasms is of great significance for improving human nutrition and health. In this study, the application of CRISPR/Cas9 technology was investigated for precise multi-target editing within the SBEIIb promoter, aiming to generate valuable germplasm resources enriched with RS. The results revealed extensive mutations in the SBEIIb promoter region, resulting in a varied reduction in SBEIIb expression levels. Remarkably, the grains from the homozygous T1 mutant lines displayed a substantial elevation in RS content, ranging from 3 to 12 times greater than that of the wild-type, accompanied by notable alterations in the starch granule morphology of these grains. This study presents an effective breeding strategy for the precise enhancement of RS content and establishes a foundation for further insights into the molecular mechanisms governing cis-element regulation of RS synthesis.