Abstract
Foods high in resistant starch (RS) are beneficial to prevent various diseases including diabetes, colon cancers, diarrhea and chronic renal or hepatic diseases. Elevated RS in rice is important for public health since rice is a staple food for half of the world population. A japonica mutant ‘Jiangtangdao 1’ (RS = 11.67%) was crossed with an indica cultivar ‘Miyang 23’ (RS = 0.41%). The mutant sbe3-rs that explained 60.4% of RS variation was mapped between RM6611 and RM13366 on chromosome 2 (LOD = 36) using 178 F2 plants genotyped with 106 genome-wide polymorphic SSR markers. Using 656 plants from four F3∶4 families, sbe3-rs was fine mapped to a 573.3 Kb region between InDel 2 and InDel 6 using one STS, five SSRs and seven InDel markers. SBE3 which codes for starch branching enzyme was identified as a candidate gene within the putative region. Nine pairs of primers covering 22 exons were designed to sequence genomic DNA of the wild type for SBE3 and the mutant for sbe3-rs comparatively. Sequence analysis identified a missense mutation site where Leu-599 of the wild was changed to Pro-599 of the mutant in the SBE3 coding region. Because the point mutation resulted in the loss of a restriction enzyme site, sbe3-rs was not digested by a CAPS marker for SpeI site while SBE3 was. Co-segregation of the digestion pattern with RS content among 178 F2 plants further supported sbe3-rs responsible for RS in rice. As a result, the CAPS marker could be used in marker-assisted breeding to develop rice cultivars with elevated RS which is otherwise difficult to accurately assess in crops. Transgenic technology should be employed for a definitive conclusion of the sbe3-rs.
Highlights
Starch is the major dietary source of carbohydrates which is composed of two types of molecules, amylose (Am) and amylopectin (Ap) [1,2]
This distribution indicated that the responsible quantitative trait loci (QTL) were few for resistant starch (RS) inheritance, and the mutated high RS locus was recessive to regular-low RS
Cultivar improvement for resistant starch Mapping genes or QTL and development of markers are essential for marker-assisted breeding (MAB), especially for RS for which assessment is extremely difficult in vivo [24], and questionable in vitro [24,25]
Summary
Starch is the major dietary source of carbohydrates which is composed of two types of molecules, amylose (Am) and amylopectin (Ap) [1,2]. RS has similar physiological functions to those of dietary fiber, and is completely resistant to enzymatic digestion in the human small intestine. Diet-related noninfectious chronic diseases including coronary heart disease, certain cancers (especially of the colon and rectum), and diabetes are major causes of morbidity and mortality world wide [10]. These unique physical functions of RS have received increasing attention from plant researchers in recent years
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