Molecular Evolution Of Key Enzymes Of Saccharomyces Cerevisiae In Wild Rice

Starch is not only a vital component of our diet, but also a kind of importantcommercial product. Starch is playing a more and more important role in people’sdaily life. Starch consists of two kinds of homopolymers: the basically linear amyloseand the branched amylopectin. The ratio of amylose and amylopectin influences thetaste, viscosity, gelatinization and retrogradation of the starch in the rice endosperm.High-amylose starches are generally widely used for commercial purposes, whilehigh-amylopectin starches have more broad application prospects in edible. In recentyears, using genetic methods to manipulate the molecular composition of starch hasbecome a new trend of development.Wild rices with CCDD genome are species that genomes have been duplicated byallopolyploization. The plants are high, containing abundant of genetic resourceswhich are useful to genetic breeding and quality improvement of rice. In order tounderstand the evolutionary rules of classical metabolic pathway in polyploids, weselected the rice species with CCDD genome (O. alta, O. grandiglumis and O.latifolia), and two related diploids (O. officinalis and O. australiensis) as researchmaterials. Because the study background of rice starch synthesis pathway is clear, wetake it as an example to show the basic evolutionary modes of different duplicatedgenes in same metabolic pathway. Five key enzymes in amylopectin synthesispathway, namely the pyrophosphorylase large subunit (AGPL2), pyrophosphorylasesmall subunit (AGPS2b), starch branching enzyme (SBEIIb), starch synthase (SSIIa)and starch isomerase (ISA1) were selected in this study. The main results were as thefollows:1. The study successfully amplified partial gene fragments of five enzymes of thethree species by PCR, and then separated the C and D genomic homologues bymolecular cloning and sequencing. The results showed that,3genes had beenduplicated in the three polyploids, and2genes were conserved one parentalhomologue with divergent evolutionary patterns. The AGPS2b genes in three specieswere all retained the homologues of the C genomic type, whereas the SBEIIb geneswere only retained the homologues of the C genomic type in species O. alta and O.latifolia, but the homologues of the D genomic type in species O. grandiglumis. Inaddition,3duplicated genes, the levels of nucleotide divergence within same genomictype in the three species were low (θw=0.00000~0.00986). The sequences variationsbetween homologues in the three species were not consistent, which depended gene itself. For example, the polymorphism level of C genomic homologues of gene ISA1and SSIIa was about1.5times or more than6times the higher than its D genomiccounterparts, respectively; while the polymorphism level of D genomic type ofAGPL2was about1.6times the higher than C genomic type.2. By calculating the select pressures of the4genes AGPL2, AGPS2b, ISA1andSSIIa detection, we found that AGPL2, AGPS2b, ISA1were all subjected to purifyingselection, whereas SSIIa was subjected to strong positive selection. In addition,inconsistent selection pressures were revealed between C and D genomic homologuesof gene AGPL2and SSIIa, whereas equal ω values were found for both homologuesof gene ISA1.