Genetic And Molecular Structural Basis For Resistant Starch And Other Functional Properties In Rice(Oryza Sativa L.)

Rice?Oryza sativa L.?is one of the most important staple crops in the world,and its high yield and good eating and nutritional quality are vital to human life.With the development of the national economy and structural reform of the agricultural supply side,rice grain quality has attracted more attention for consumers and breeders.Starch is the predominant energy storage substance in rice and has crucial influence on its quality.However,the molecular structural basis and genetic mechanism underlying rice digestion and other functional characteristics are not clear,which restricts the improvement of rice quality and the application of rice starch.This study systematically focuses on the relations among genetics,structure and functionality in rice digestion and other functional characteristics,and provides a new theoretical basis for the targeted breeding and improvement of rice quality.The main conclusions are as follows:1.The quantitative trait loci?QTL?of rice starch digestion characteristics was identified by using genome-wide association analysis?GWAS?.The content of resistant starch?RS?had a significantly positive correlation with the apparent amylose content?AAC??r2= 0.7529?in the whole association panel.Four QTLs for RS were detected,and each could explain 10-13% of total phenotypic variation.One QTL?chr06₁765761?was directly on the Wx genes,while other three were near the SSIIa on chromosome 6 chr06₆168586),ISA1 on chromosomes 8?chr08₂3391108?and AGPS1 on chromosome 9?chr09₅975264?,respectively.2.The relations between starch fine structure and functional characteristics were analyzed with the high amylose indica rice GLA4 and its mutants,and the dynamic gene expression patterns involved in starch synthesis during seed development were also determined.The results showed that the AAC of the mutants GM03 and GM04 was 33.5% and 35.1%,and the RS content was 7.9% and 8.4%,respectively,which were significantly higher than those of the parent and other mutants.The height at peak of amylose?h AM?was higher in GM03 and GM04,which indicated that the true amylose content?TAC?was also significantly higher than others.The expression levels of GBSSI at 5 days after flowering?DAF?and SSI at 15 DAF had positive correlation with AAC,TAC and amylose fine structure,but had negative correlations with most of the amylopectin fine structural parameters.Therefore,the amylose content and fine structural parameters had positive correlation with RS,whereas fb1 amount of amylopectin chain length distribution?CLD?had positive correlation with the RS,the average chain length and fb3 amount had negative correlation with RS.3.The relations among starch biosynthesis related protein content,starch fine structure and functional characteristics were analyzed in a low amylose indica rice 93-11 and its mutants.The results showed that JM2 had TAC of 26% and RS of 3%,which was significantly higher than that of the parent and other mutants.The relative content of GBSSI and SSIIIa in JM2 averaged 3.67 and 8.10,respectively,which were significantly higher than others.GBSSI and SSIIIa could affect h AM directly,while h AM was shown to be correlated with AAC,RS,hardness?HD?,cohesiveness?COH?,onset temperature?To?,enthalpy of gelatinization??35?Hg?,enthalpy of retrogradated starch??35?Hr?,and percentage of retrogradation?R%?.The SSI,SSIIa and SSIIIa affected the amylose size?Rh,AM?,which was correlated with the AAC,TAC,RS,HD,COH,To and Tp.Furthermore,both SSIIa and PUL affected the XAP2,and XAP2 was correlated with the To.These results indicated that starch biosynthesis-related enzymes could affect starch fine structure by regulating the synthesis of starch and thus affect the functional characteristics such as RS content.4.The RS content in high RS rice mutants could further be increased through pullulanase modification,heat-moisture modification or citric acid modification.Except for 93-11,the RS content of citric acid modified samples was higher than other treatments.One amylose extender?ae?mutant?BP577I?modified with citric acid had the highest RS content of 15.74% among all samples.The RS content of 93-11 modified by pullulanase reached 6.11%.In the modified starch,RS had significantly positive correlations with AAC and RC,and significantly negative correlations with the melting temperature?To L,Tp L,Tc L?of the starch-lipid complex.This research provided a new idea for the development of specific starch with high RS.