| Rice as an important grain crop is indispensable for safeguarding national food security and maintaining social stability.Improving the morphological characteristics of the panicle is an effective way to increase rice yield.Panicle length is usually measured as the yield-related trait closely linked to panicle architecture,largely determined by quantitative trait locus（QTLs）of multi-gene.Therefore,analysis of the major QTL for panicle length and the relationship with other traits can directly provide an effectively theoretical basis for rice molecular breeding.With the maturity of gene mapping methods,some panicle length-related genes have been cloned,even a few QTLs have been successfully applied to practice.Based on the genetic background of heavy panicle hybrid rice Shuhui498（R498）,F771 with long panicle length architecture was obtained by crossing R498 and CT11327.The F2 segregation population generated from a cross between F771 and R498 were used to QTLs analysis.The main results are as follows:1.Compared with R498,F771 showed higher plant height,and panicle length,primary and secondary branch numbers respectively increased by 32.0%,12.1%and23.5%,resulting in a 39.0%increase in spikelet number per panicle（SPP）.However,the1000-grain weight decreased by 21.0%,mainly due to a 2.0%and 6.7%reduction in grain length and grain width.2.Scanning electron microscopy analysis indicated that the development of F771 was slower than R498,which increased the elongation of branches and rachis and delayed the transition time from branch to spike.That is why more SPP and longer panicle length are observed in F771 than R498.3.The panicle length of BC5F1 plants by backcrossing of F771 and R498 exhibited intermediate type,indicating that was a semi-dominant inheritance pattern.The BC5F2panicle length separated populations showed a continuous normal distribution predicting the multiple panicle length QTLs.There was a significant linear correlation between panicle length and SPP,but no correlation with plant height,grain size and 1000-grain weight,so that the panicle length single segment substitution plant could be isolated.4.We applied the BSA and overlapping segment localization method for gene mapping,and identified two linkage regions on chromosome 10 and 2 from the BC5F2segregation population,named as qPL10 and qPL2,respectively.qPL10 was mapped on the 615kb fragment,in which LOC＿Os10g33780（TAWAWA1）as one of candidate gene.5.There’s no difference in TAWAWA1 CDS of R498,F771 and Nip,but in promoter.Compared with R498,GCG and GCGGCG was inserted into F771 and Nip.TAWAWA1 can be divided into the three genotypes in the natural population of our laboratory.Moreover,q-PCR showed an increased expression level of this gene in the fragment substitution line.It was confirmed that TAWAWA1 may be related to panicle length phenotype.6.The CDS and promoter of TAWAWA1R498,TAWAWA1F771 and TAWAWA1Nip were transferred into ZH11 respectively.The panicle length of positive plants in TAWAWA1Nip T1generation decreased by 38.1%and SPP dropped an average of 30.2%compared with ZH11.However,there’s two phenotypes in the T0 generation positive plants of the complementary TAWAWA1F771.One was similar to TAWAWA1Nip,while the other showed longer panicle length and more SPP compared with the control.It may be related to the sequence of TAWAWA1Nip contained in ZH11.So,further research in the T1 generation is needed.Two target sites on promoter and the exon of TAWAWA1 under the background of ZH11 were edited by using the Crispr/cas9 system,and a total of 4 different mutation patterns were detected in T0 plants.Homozygous knockout plants will be used for re-transferred the three genotypes of TAWAWA1 to confirm whether TAWAWA1 is qPL10.7.The polymerization analysis observed that the panicle length of qPL10/qPL2 was36.9±1.77cm,which was 3.0%～21.6%（P<0.01）longer than qPL10,and increased by1.0%～12.5%（P<0.05）compared with qPL2.So qPL10/qPL2 showed an additive effect on panicle length compared with a single QTL. |
