An Insight into the Glycemic Index of Rice

Glycemic index of rice is a highly complex trait. Rice varieties possessing slowly digestible starch (high amylose) are potentially characterized to have low glycemic index and can be useful for management of type II diabetes. Understanding genetic mechanisms underlying starch biosynthesis and metabolism of cooked rice can pave the way for developing efficient breeding and selection strategy for combining high grain yield with low glycemic index. In this context, reverse genetics can prove useful. Available rice genome sequence information encoding key enzymes involved in biosynthesis of amylose component of starch can unravel novel alleles involving single nucleotide polymorphisms (SNPs). A multi-allelic waxygene (Wx) encoding Granule-Bound Starch Synthase I (GBSS I) enzyme is known to determine amylose content in rice endosperm. Potential molecular markers are now available to detect GBSS I alleles (SNPs) associated with five classes of amylose (waxy: 0–5%, very low: 5–12%, low: 12–20%, intermediate: 20–25%, and high:25–33%). These can be routinely used to assist breeding programme. Besides, the presence of intra-class variations in amylose content could be attributed to additional regulatory elements or environmental conditions.