Genetic Diversity Of Wx Gene And Its Effect On The Main Physical-chemical Quality In Rice

Rice is one of the main food with largest population in the world. Since the development of economic society, people has enhanced the requirement of rice with good grain quality. Among the determinants of rice grain qualities, amylose content is considered as the most important factor for rice cooking and eating quality. In rice, the Waxy （Wx） gene is responsible for amylose synthesis, and, therefore, it is very important to realize the relationship between the diversity of Wx gene and rice grain quality. It will provide the theoretical and practical bases to mine novel Wx alleles and subsequently improve rice grain quality. In present study, we collected 277 rice germplasms from all over the world, and the sequence diversity of Wx gene and main grain qualities were analyzed. Subsequently, the correlation between Wx gene’s diversity and grain quality was also analyzed. The main results are as follows.（1） The whole Wx gene from all 277 rice materials were sequenced and compared, and the results revealed that there were 66 mutation sites among these germplasms, and the Wx gene’s nucleotide diversity is not remarkable. All these Wx sequences were belonged to 6 known Wx alleles, including Wx^a, Wx^b, Wxⁱⁿ, Wx^op, Wx^mp and wx. The rice materials containing the Wx", Wx^b or Wx’" allele accounts for 95% of the total population. The clustering analysis showed that all the Wx alleles could divide into 2 groups, the sequences of Wx^b, Wxⁱⁿ, Wx^mp and wx were similar and belong to group A,while the sequences of Wx^a and Wx^op were similar and belongs to the group B.（2） The amylose content and RVA profile of mature seeds were measured, and carefully compared. The results showed that the amylose content had a wide distribution, but most of the rice materials contains the amylose content between 15-25%. The RVA profile also had a wide distribution and the variable coefficient was more than 20%. The clustering analysis of tested grain qualities implied that the tested rice germplasms could be divided into two groups with five subgroups, named as subgroup CI,CII, DI, DⅡ-a and DⅡ-b. The study by correlation analysis showed that it has highly significant correlation between the amylose content and RVA profiles, including HPV, BDV, CPV, SBV, CSV and PeT. It is implied that the change of amylose content will have a great effect on the RVA profile.（3） The relationship between Wx sequence diversity and grain quality was finally analyzed, and the resulted showed that the amylose content controlled by different Wx alleles was quite different. The contribution to amylose content is Wx^a>Wxⁱⁿ>Wx^b>Wx^op>WxmP>wx. Based on the combination of the characteristic values of amylose content and RVA profiles, it could be indicated that the contribution to rice cooking and eating quality might was Wx^op>Wx^b>Wx^mp>Wxⁱⁿ>Wx^a. The amylose content is obviously different between the two Wx gene groups, which is classified by clustering analysis. The amylose content is 16.91±4.32% for group A, while it is 23.24±4.23% for group B. The correlation analysis between Wx mutation sites and rice quality implied that there are three sites important for rice quality, which are all located in the exons of Wx gene. The analysis of relationship between Wx haplotypes and grain quality showed that the different sequence of Wx gene had an effect on the rice grain quality.