Low Starch Viscosity In Rice: Physicochemical Properties And Gene Mapping

Starch is the most storage component in rice endosperm, and it is considered as the key determinant of rice grain quality. In rice quality improvement programs, starch pasting viscosity, which can be measured by the Rapid Visco Analyzer (RVA), serves as an important index in estimating the eating quality of rice. Therefore, fine mapping and cloning the genes controlling starch viscosity would undoublely play important roles in improving and underlying the formation mechanisms of rice quality. In our previous study, we had found an indica cultivar named S13 showing an extremely low RVA profile but its apparent amylose content (AAC) was nearly the same with the commom indica cultivars.In our study, the map-based cloning technique was used to map the LSV (Low Starch Viscosity) gene which contributed to the low starch viscosity. Besides, the effects of the LSV gene on the physicochemical properties and starch structure were preliminariely analyzed by using the constructed near isogenic lines (NILs).1. To analyze the inheritance of the low viscosity, F1 hybrid crossed from S13 and different cultivars were generated and the RVA profiles of the grains from each F1 individuals were measured and compared with their parents. The results showed that the low starch viscosity is dominant, or partial dominant, and might be controlled by one gene or major QTL. Moreover, the inheritnace of each RVA parameters was analyzed among the S13/Nipponbare derived F2 population, and the results showed that the low starch viscosity might be caused by the low peak viscosity (PKV), breakdown value (BDV) and setback value (SBV), which were also controlled by the dominant LSV gene.2. Through the bulked segregant analysis (BSA) in F2 generation with 46 molecular markers, we preliminariely mapped the LSV gene on the short arm of chromosome 6. Then, by using constructed near isogenic lines (NILs), we further mapped the LSV locus between two molecular markers RM586 and RM587, and the physical distance between these two markers was about 800kb. In which, the rice Wx gene is also located.3. With the indica cultivar S13 as the donor parent and the japonica cultivar Nipponbare the recipient parent, a NIL containing the LSV gene from S13, named LSV and showed low viscosity,, was constructed. Meanwhile, another NIL containing the fragment with the Wxa locus from Longtefu (LTF), named HSV and showed normal starch viscocity, was also selected as a control. Both NILs were in BC4F3 generation. The results from the analyses of physicalchemical properties and starch structure revealed that, besides the low RVA profiles, the gel consistency (GC) and thermal parameters were significantly different between the LSV and HSV. But, the apparent amylose content (AAC), the expression of the Wx protein and the starch structure were nearly showed no difference between these two individuals.