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Critical roles of soluble starch synthase SSIIIa and granule-bound starch synthase Waxy in synthesizing resistant starch in rice
Friday, 2016/11/11 | 08:43:29
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Hongju Zhou, Lijun Wang, Guifu Liu, Xiangbing Meng, Yanhui Jing, Xiaoli Shu, Xiangli Kong, Jian Sun, Hong Yu, Steven M. Smith, Dianxing Wu, and Jiayang Li SignificanceResistant starch (RS) has the potential to protect against diabetes and reduce the incidence of diarrhea, inflammatory bowel disease, colon cancer, and chronic renal and hepatic diseases. In this study, we identified two critical starch synthase genes which together regulate RS biosynthesis in rice, and we explored their potential interactions as part of a network of starch biosynthetic enzymes. The findings hold promise for applications in breeding varieties with improvement of RS in hot cooked rice and may also have general implications for understanding RS biosynthesis in other major cereal crops. AbstractChanges in human lifestyle and food consumption have resulted in a large increase in the incidence of type-2 diabetes, obesity, and colon disease, especially in Asia. These conditions are a growing threat to human health, but consumption of foods high in resistant starch (RS) can potentially reduce their incidence. Strategies to increase RS in rice are limited by a lack of knowledge of its molecular basis. Through map-based cloning of a RS locus in indica rice, we have identified a defective soluble starch synthase gene (SSIIIa) responsible for RS production and further showed that RS production is dependent on the high expression of the Waxya (Wxa) allele, which is prevalent in indica varieties. The resulting RS has modified granule structure; high amylose, lipid, and amylose–lipid complex; and altered physicochemical properties. This discovery provides an opportunity to increase RS content of cooked rice, especially in the indica varieties, which predominates in southern Asia.
See: http://www.pnas.org/content/113/45/12844.abstract.html?etoc PNAS November 8 2016; vol.113; no.45: 12844–12849
Fig. 1. Characterization of the RS mutant b10 and positional cloning of the B10 gene. (A) Plant phenotype of the wild type (R7954) and the high-RS mutant (b10). (B) RS contents of grains from R7954 and b10 and from plants carrying different SSIIIa alleles in an F2 population from a cross between R7954 and b10. Error bars represent ±SEM (n = 62). Different letters above bars indicate significant differences at P < 0.05, using Tukey’s multiple comparison test. (C) Mapping of the target gene between the markers M6 and M8 on the short arm of chromosome 8. Numbers below the lines indicate the number of recombinants between the locus and the markers shown. (D) SSIIIa gene structure and mutation site. Filled boxes indicate exons (numbered 1–16) of SSIIIa. Site of the mutation from G to A in SSIIIa of b10 is shown in the open box above exon 6. Nucleotide sequences of the junction between intron 5 and exon 6 in R7954 and b10 are shown in Lower, with deduced amino acid sequences. The mutated nucleotide in b10 is shown in red, together with the loss of original 3′ splice site and creation of a new 3′ splice site. The mutation generates a recognition site for MluC I (AATT), which is used to generate a CAPS marker (Fig. S1) to determine genotypes of the plants shown in B. |
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