| Rice is the main grain for Chinese people and most of the population in the world.With the increase of population and industrial consumption,the need and the consumption gap will mount up constantly.Therefore,high-yield breeding is still the main focus of genetic improvement of rice varieties at present and in the future.Rice yield is mainly composed of three elements:number of panicles per unit area,number of filled grains per panicle and 1,000-grain weight.The number of panicles consists of basic plant number,tiller number per plant and percentage of earring-tillers.When the former is constant,the latter two are important determinants of the number of panicles per mu.As a result,studying the genetic mechanism of rice tiller number and percentage of ear-bearing tiller can lay a solid theoretical foundation for creating breeding materials or varieties with more tillers and higher percentage of ear-bearing tiller,and is instructive to high-yield breeding of rice.In this study,a mutant W33 with higher-nodal-position tillers and high percentage of earring-tillers of wild-type rice restorer line R818 serves as the test object.Based on the phenotypic identification of agronomic traits,the genetic expression form of higher-nodal-position tiller traits is studied by analyzing the hybrid segregative generations,and the higher-nodal-position tillering genes are mapped by leveraging the map-based cloning technology.The study results are as follows:1.During the seedling stage,the ground and underground parts of mutant W33 grow normally,and its phenotypic characteristics such as plant height,leaf size,root number and root length are not significantly different from those of wild type R818.After the jointing stage,the two plants gradually show difference in plant height,and the upward growth speed of R818 is obviously faster.The plant height of R818 is greatly higher than that of W33 at the heading stage,and the heading stage of R818 is 1318 days earlier than that of W33.2.In the tillering stage,the tillering rate of W33 is far faster than that of R818.After the booting stage,the tillering buds of R818 are dormant gradually until they stop,while the tillering buds of the main stem and the nodes below the neck-panicle nodes of tillering panicles of W33 are still active.In the end,the average tiller number per plant of W33 is8.8 times that of R818,the average effective number of panicles is 8.6 times that of R818,and the average percentage of earring-tillers is equivalent to that of R818,but the length of single panicle,the number of branches per panicle and the number of grains per panicle are much lower than that of R818,while the 1,000-grain weight is slightly different from that of R818.3.The results of yield comparison test show that the grain yields per plant of W33 and R818 decrease as the density increases.When the density is the lowest,the grain yield per plant is the highest;and vice versa.Although the yield per panicle of W33 is much lower than that of R818,W33 and R818 show no significant difference in population yield under the same density(Fvalue 1,5=3.7868<F0.05).Within a certain density range,W33 can give full play to its advantages in tillering ability and percentage of ear-bearing tiller to make up for its disadvantage（low yield per panicle）,and its population yield finally reaches the level equivalent to that of R818.4.W33 self-bred progenies were no segregation in higher-nodal-position tiller traits,and they were genetically stable.（W33×R818）or（R818×W33）F1 showed no higher-nodal-position tiller;the backcross progenies of（W33×R818）or（R818×W33）F1generation and W33 showed two phenotypes,i.e.without higher-nodal-position tiller and with higher-nodal-position tiller,at a segregation ratio of 1:1,and the segregation ratio of such two phenotypes in F2 generation of（W33×R818）or（R818×W33）was 3:1.The results indicated that the inheritance of higher-nodal-position tiller traits of W33 was controlled by a pair of recessive nuclear genes,and W33 was a recessive mutant of this gene.5.Using the DNA of the extremely mutated isolated plant.W33 higher-nodal-position tillering genes are preliminarily located between two markers（RM53 and RM145）which are located on chromosome 2 by means of SSR.The region is about 3.3M long in total.BSA is used to further reduce the region to 1.7M,and the indel found in re-sequencing is applied to re-develop a new marker,reducing the target gene region to 262Kbp of5563847bp-5826131bp.According to the rice gene annotation,17 candidate genes are found in the section,the gene function annotation is carried out on the 17 candidate genes by referring to databases such as InterPro,GO,KEGG,Swissprot and TrEMBL.Afterwards,ninegenes（7687-TA,7688-TA,7691-TA,7695-TA,7701-TA,6989-TA,6988-TA,6986-TA and 6984-TA）are targeted and then analyzed by RT-qPCR,and finally the candidate genes are selected from 7688-TA,7691-TA,and7701-TA. |
