Map-based Cloning And Function Analysis Of MμLTI-SPIKELET PANICLE(MSP) Gene In Rice(Oryza Sativa.)

Rice is the model plant for studying monocot,and it is also one of the three major food crops in the world.Yield is the core target of rice breeding,and ―grains per panicle‖is one of the most important factors in the composition of yield.A variety of ―spikelet morphological traits‖ including branch numbers and lengths and the density of spikelets which will eventually affect the number of grains per panicle and thus affect rice yield,and flower organ morphology will also affect rice yield.Therefore,the development of rice flower spikelet is closely related to yield,and related research is of great significanceIn this study,we identified a mutant on rice panicle development,named mμlti-spikelet panicle(msp).We characterized in detail the phenotype of msp by morphological and histological observation and the mutant gene by map-basd cloning.Furthermore,we characterized the gene‘s fuction and expression profile and the regμlation mechanism.Main conclusions are as follows;1.Morphological and histological analysis of msp mutantThe inflorescence produced more primary and secondary branches in lower nodes than the wild type,which increased the total number of spikelets to an average of 274 per panicle far more than 188 per panicle of wild type.Although the 100-grain weight of the mutant went down due to the smaller grain size,the mounting number of spikelets per panicle still increased the yield per plant of the msp mutant significantly.The phenotype observation and histological analysis of the spikelets on msp mutant and wild-type spikelets revealed that the sterile Lemma of msp also exhibited elongation and the homeotic transition into lemma and palea body compared with the wild-type;Also the rudimentary glume exhibited the homeotic transition into the sterile Lemma or lemma compared with the wild-type.2.Gene mapping of MSP genemsp was roughly mapped to a single locus on the chromosome 3.between the two SSR(RM6781&RM15937).3.Map-based cloning of MSP geneFollowing genome sequencing and mutant complementation analysis the MSP gene was found to encode Os MADS34 protein.The 134 th codon of CDS changed from T to A caused the changing of 45 th amino acid which located in the MADS-BOX conserved domain.Further constructing the vector(PCAMBIA1301-35 s Os MADS34CDS-NOS)which was transformed into msp callus,we ensure the MSP is Os MADS34 because of nomal transformant.4.Expression profile of MSP geneWe characterized the expression profile of MSP in rice,funding high expression in young panicle,sterile lemma,rudimentary glume and pistil,a little bit lower expression in tiller bud and stamen,weak expression in root,cμlm,leaf and other flower organs.5.Q-PCR analysis of panicle and flower development related genesSome genes involved in initiating and/or maintaining branch development,such as MOC1,Os CKX2/Gn1 a,and TAW1 are up-regμlated in msp young panicle and MSP protein has transcriptional repressive activity,suggesting that Os MADS34 may play a regμlatory role of these known genes,thereby regμlating the thransform of inflorescence meristem to spikelet meristem;at the same time,the Q-PCR analysis of floral organ identity genes showed that the higher expression of DL than wild type in sterile lemma and rudimentary glume,indicating MSP involved in regμlating sterile lemma and rudimentary glume identity development.6.Molecμlar mechanism of regμlating the development of inflorescence architecture in rice by MSPOs MADS34 belongs to the transcription factors of MADS Box family.The resμlts indicate that Os MADS34 has transcriptional repressive activity through Dual luciferase reportor system experiments(DLR).It was found that Os MADS34 can interact with the transcription co-repressor LEUNIG and TOPLESS,and probably to recruit histone deacetylases to repress transcription of target genes thus affecting inflorescence architecture development.