Genomics and molecular breeding of soft rice- a locally evolved japonica line with unique ready-to-eat trait

Abstract

Low amylose containing parboiled soft rice is a natural wonder having ready-to-eat trait (RTE) with possible risk of high glycemic response (GR). In this present investigation typical Indian soft rice (var. Vogali Bora) was studied for biochemical basis, whole genomic and transcriptomic dissection followed by molecular breeding for improvement of yield and GR. Quantitative estimation showed that lower amylose (AC) to amylopectin ratio with low resistant starch (RS) in soft rice may be the possible biochemical basis of softness and high GR. Presence of a smaller number of SNPs in WAXY locus and significant down regulation of GBSSI loci supported the molecular basis of lower AC of soft rice like japonica sub varieties. But in comparison to normal rice higher number of SNPs in starch synthesis related genetic loci conferred that they are specially evolved for unique type of starch synthesis to acquire RTE trait which is further propped up by down regulation of a cascade of trait linked transcripts during grain filling. With respect to soft rice, inbreed lines showed improvement in yield related traits and better GR in mice model due to improved AC and RS content of F2:3 seeds. Though this group of rice is of japonica in origin, due to presence of unique type of sequence diversity and starch synthesis machinery, they possess RTE trait which is unique in rice and rice relatives. It made this study significant and in future, generation advancement of developed inbreed lines may produce healthy soft rice on a large scale.