| Starch is the main component of dry matter in rice grain,and it is also an important storage material in rice grain.At the same time,starch affects the taste quality of rice,so the content,composition and structure of starch ultimately determine the yield and quality of rice.The process of starch biosynthesis in plants is a delicate and complex reaction involving a variety of enzymes,but its molecular regulation mechanism is still unknown.It is necessary to understand the related genes involved in starch biosynthesis more deeply so as to improve rice yield and quality through genetic breeding.Rice endosperm occupies most of the grain volume and is the main place for starch storage.By studying the abnormal mutant of rice endosperm,we can not only understand the process of starch biosynthesis,but also improve the quality of rice.Identification of new mutants involved in starch synthesis,metabolism and amyloplast development is of great significance to comprehensively elucidate the molecular mechanism of starch synthesis and amyloplast development.In this study,a stable endosperm mutant named w4730 was screened from the mutant library of Japonica rice cultivars treated with 1-methyl-1-nitroso-urea(MNU)mutagen.The morphological characteristics and physicochemical properties of endosperm were analyzed,and the endosperm internal structure was observed by scanning electron microscopy.A hybrid combination of w4739 mutant and Nanjing 11 was prepared.The W4730 gene was located by map cloning technique.The results showed that the mutant gene was a gene involved in rice endosperm development,and it could affect the starch synthesis pathway in rice endosperm.The main results are as follows:1.The endosperm appearance of mature grains of mutant w4730 after removing shell showed white phenotype without obvious shrinkage.Compared with the wild type,the grain length and width of w4730 did not change significantly,but the grain thickness and 1000-grain weight decreased significantly.2.Scanning electron microscopy(SEM)showed that the starch granules of wild Ningjing 4 had a compact polyhedron structure and uniform size.The starch granules in the center of endosperm of mutant w4730 were different in size,loosely arranged and interstitial.The starch granules at the endosperm margin of mutant w4730 were similar to those of wild type Ningjing 4.Cytological observation showed that the mutant had abnormal amyloplast development in the endosperm.3.The total starch,fat and protein content of mutant w4730 had no significant difference.But the amylose content decreased significantly.At the same time,the hot paste viscosity(HPV),cold paste viscosity(CPV),maximum viscosity(PKV)of starch in mutant w4730 were lower than those of wild type,and the solubility of rice flour in urea solution was lower than that of wild type.4.At the same time,the distribution of amylopectin length in mutant w4730 changed.Compared with wild type,the branching ratio of mutant w4730 with DP 15-35 increased,while that of DP 7-15 decreased.5.Using the F2 population of w4730/Nanjing 11,the W4730 locus was located on the short arm of chromosome 4.The marker I4-13 and N4-40 were in the 3 Mb interval.Sequencing showed that four base deletions occurred in Os04g0645100 genewhich leads to the early termination of translation process·Wx is a major regulator of amylose content in rice and plays a decisive role in cooking and eating quality of rice.The difference of amylose content among rice varieties is mainly caused by the allele variation of Wx gene.The identification of allelic variation types of Wx gene is an important way to improve rice taste quality.In this study,83 soft rice resources were identified.A new mutation site was found by sequencing.In exon 10,115 base C mutated to T,CCT mutated to TCT,resulting in 415 amino acids mutated from proline to serine.According to the difference of base at 5’end,two alleles Wxth and Wxhn can be classified.The newly discovered multiple allele can regulate amylose content and improve rice quality. |
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