Moderate Regulation of SBEIIb Gene Expression by Editing Cis-Regulatory Elements Enhances the Resistant Starch...

Area of Science:

• Plant Biotechnology
• Nutritional Genomics
• Agricultural Science

Background:

• Rice is a global staple food, and increased resistant starch (RS) content offers potential health benefits for preventing diabetes and hyperlipidemia.
• Previous attempts to increase RS in rice led to undesirable agronomic traits like reduced grain weight and altered seed morphology.

Purpose of the Study:

• To identify cis-regulatory elements (CREs) that enhance RS content in rice without compromising agronomic performance.
• To understand the molecular mechanisms underlying high RS accumulation and its impact on rice endosperm metabolism.

Main Methods:

• Utilized assay-for-transposase-accessible-chromatin sequencing (ATAC-seq), DNAase I hypersensitive site sequencing (DNase-seq), and bioinformatics analysis to identify CREs.
• Conducted starch structure analysis, transcriptomics, and metabolomics to evaluate the effects of identified CREs on rice endosperm.
• Performed genetic studies to identify transcription factors binding to the CREs.

Main Results:

• Identified two CREs associated with the SBEIIb gene, leading to a ~5.31-fold increase in RS content in mutant rice lines.
• Observed no adverse effects on starch morphology, grain shape, or major agronomic traits in the high-RS mutants.
• Found that increased medium- and long-chain amylopectin contributed to the high RS phenotype and noted minor metabolic pathway alterations.

Conclusions:

• The identified CREs offer a strategy for developing high-RS rice varieties with improved health benefits without detrimental agronomic consequences.
• Transcription factors NAC20, NAC23, and NAC26 were found to co-regulate SBEIIb gene expression via binding to the identified CREs.
• This research supports the development of healthier rice and potentially other cereal varieties with enhanced RS content.