QTL Analysis And Mutant Gene Mapping Of Tillering And Leaf-related Trait In Rice (Oryza Sativa L.)

People depend on rice as a major food resourse makes rice one of the most important crops,and what's more,a small genome size,a known genome sequence,easy for Agrobacterium-mediated genetic transformation and genome synteny between rice and other grasses make rice a model monocotyledon plant.Because of this importance of rice in social life and biological research,the screening for elite germplasm and research on various biological processes have never stopped;especially rice yield-related traits and biological processes.Among these biological processes,tillering and photosynthesis are undoubtedly very important;tiller number and photosynthetic-related characters show great association with rice yield.At the same time,the rapid development of molecular biology provides a mature and convenient solution for studying certain traits or biological phenomenons.Construction of mutant library,QTL analysis and map-based cloning,and other platforms are mature and widely popular,so that the biology of rice entered a new period.Based on such a background,QTL analysis for tiller number and photooxidiation tolerance was carried out to clarify,the genetic characteristics of these traits and to provide available molecular markers for the practice of molecular breeding. Relying on huge number rice mutants in our lab,we identified a number of few-tillering and leaf color-related mutants,and map-based cloning strategy was used to mapping the caused genes.All these researches shed light on the study on molecular mechanism of tillering and photosynthesis.The following is a brief introduction of the relevant research, the progress and the significance of these studies:1 In the present study,in order to systematically dissect the genetic mechanism of rice tilling for the super rice standard mould and the model system of branching development, two ethyl methane sulfonate-induced rice(Oryza sativa L.) reduced -culm-number(rcn) mutants from the progeny of Nippobare(O.sativa ssp. japonica),namely rcn8 and rcn9,were used.Their maximum tillers were both less than 4.In addition,rcn9 had another major feature of rust-spotted leaves.Allelic tests between these two mutants and seven other recessive few-tiller mutants revealed that they were previously unknown loci.Genetic analysis showed that the rcn traits were all controlled by a pair of different recessive genes,designated as RCN8 and RCN9,respectively.Two F₂ populations derived from crosses between the rcn8 or rcn9 mutants and 93-11 was constructed.Linkage analysis using two rcn F₂ mapping populations with published simple sequence repeat markers demonstrated that the RCN8 and RCN9 genes were mapped on the long arm of chromosome 1(119.6 cM) and the short arm of chromosome 6(63.6 cM),respectively. The results of the present study were beneficial to map-based Cloning and functional analysis of the RCN8 and RCN9 genes.2 Culm-tillering dynamic is used as a vital agronomic index and is a very important physiology phenomenon in rice development.The objective of this study was to investigate the genetic basis of the culm-tillering dynamic of rice.Two different DH populations,one was derived from a cross between japonica rice JX17 and indica rice ZYQ8,including 127 lines and the other with 120 lines was derived from a cross between japonica rice CJ06 and indica rice TN1(herein designated as DH-1 and DH-2,respectively) were used for unconditional,and developmental quantitative trait locus(QTL) mapping of culm-tiller-number at different growing stages. The whole genome comparative QTL mapping was also conducted.44 conditional and unconditional QTL were detected in 10 chromosomes except chromosomes 3 and 12 from DH-1 population,while When 70 conditional and unconditional QTL were detected on 11 chromosomes except chromosome 7 from DH-2 population. And through whole genome comparative mapping,10 pairs of 26 QTL which were located in the similar physical regions were also identified.The results also showed that 6 pairs of 14 QTL loci were detected in the same development stage,and there may be major quantitative trait loci within these QTL.Although we identified resemblant QTL in the similar physical region in these two DH populations,because of the inconsistent magnitude,further investigation is still needed for the exact position and the essential of the gene. 3 In this study,a line DH78 form a double haploid(DH) population derived from a ZYQ8(indica)/JX17(japonica) crossed by anther culture was used.DH78 exhib ited dwarfism and a less-tiller(dft) character.The gene(DFT1) was mapped to chromosome 2 using a F₂ population of DH78/JX17,and more interestingly,the genomic region of DFT1 was coincided with the mapping region of the small-LOD peak,QTL ph2 and tp2,that was identified at low-nitrogen in a research carried out in our lab before.Further backcrossing and fine-mapping successfully delimited the DFT1 locus to a 91 kb region with 14 open reading frames(ORFs).4 High order tillering(HOT) is a common phenomenon in rice production,while high order tillering is an important sydrome of rice domestication.Two different DH populations,one was derived from a cross between JX17 and ZYQ8 and the other derived from a cross between CJ06 and TN1(herein designated as DH-1 and DH-2, respectively) were used to study genetic characteristics of high order tillering.Using composite interval mapping,3 QTL qHOT3,qHOT6-1 and qHOT8,located on chromosomes 3,6 and 8 respectively were identified in DH-1 population;and in DH-2 population,2 QTL were detected,which were located on chromosomes 6 and 12.Meanwhile,3 and 7 pairs of epistatie loci affecting HOT were mapped in DH-1 and DH-2,respectively.Although,no identical QTL was identified by comparative mapping,gene/genes affecting HOT must exist in chromosome 6 because QTL was detected in this chromosome by QTL mapping in both two populations.5 A rice mutant ygl3 with yellow leaf was isolated and found to be controlled by a recessive gene genetic analysis.Used F₂ population derived from cross between ygl3 and Zhonghual 1 as primary mapping population,YGL3 was mapped between SSR marker RM6874 and RM5764 on the short arm of the chromosome 2.Further more,enlarged mapping population makes the gene successfully narrowed down to a interval between STS marker STS2 and STS6 on the BAC clone OSJNBb0088N06,the physics distance was about 60 kb.Annotation reveald a chlorophyll synthesis-related gene Glutamyl-tRNA synthetase gene was in this region, Sequence analysis suggested a 3 bp deletion(GAG) which led to a deletion of an amino(Glu) might associate with the mutation phonetype.6 In present study,another yellow-green mutant ygl4 was characterized.Through map-based cloning strategy,YGL4 was located on a 250 kb region between simple sequence repeat(SSR) maker SSR1 and RM297 in chromosome 1 using 1116 mutantion individuals in a F₂ population derived from the cross ygl4/TN1.Sequence annotation suggested a candidate gene - thylakoid membrane phosphoprotein gene which was chloroplast development related,and the sequence analysis was undertaken.7 A double haploid(DH) population including 127 lines,derived from a cross between indica rice(Oryza sativa L.) Zhaiyeqing 8 and japonica rice Jingxi 17 was used to detect quantitative trait loci of tolerance to photooxidation.One QTL controlling tolerance index(TI) was detected on chromosome 1 and five QTL controlling sensitive index(SI) for photooxidation tolerance were mapped on chromosomes 1,1,6,8 and 9,respectively.Meanwhile eight pairs of epistatie loci affecthag TI and SI were also detected(three pairs for TI and five pairs for SI).Besides, 41 rice varieties were identified for photooxidation tolerance and sensitive index.In this study,QTL analysis and map-based cloning strategy were used to study rice tillering and photosynthesis-related traits,and certain results were achieved.The current findings need further study to serve rice molecular breeding,and deepen the understanding of the molecular mechanism of the tillering control,biosynthesis of chlorophyll and the development of chloroplast membrane.