Genetic Analysis Of Major QTL QKL9 For Kernel Length In Maize(Zea Mays L.)

Yield-related traits of corn are complex quantitative traits with low heritability and susceptible to environment.The yield of per unit area of maize is composed of three parts: panicle per unit area,kernel number per panicle and kernel weight,and the kernel shape is the key factor in determining kernel weight.In order to analyse the genetic basis of grain shape,the QTL-NIL population and the pure line of the target region were used to further fine mapping of the qKL9 and confirm the exact position of the QTL on the chromosome based on the early mapping of the major QTL qKL9 which affect the grain length.The main results of this study are as follows:1.Enriching markers located in the target segment.A total of 21 pairs of SSR markers that were polymorphic among the parents were screened between the C9-54 and C9-58 markers that in the original target segment,and 5 pairs of them were chosen to enrich markers located in the target segment because of their good polymorphic and clear patterns.The average density of markers was 1.5Mb after that.2.Correlation analysis of kernel length,kernel width and kernel weight.Based on the correlation analysis of phenotype of kernel length,kernel width and hundred-kernel weight in BC4F2,BC4F3 and BC5F1 populations under three environmental conditions,it was found that kernel-length was significantly and positively correlated with kernel width and hundred-kernel weight(r=0.17-0.41,r=0.40-0.66),and kernel width was significantly and positively correlated with hundred-kernel weight(r = 0.54-0.67)(P <0.01)under all environmental conditions.3.Fine mapping of qKL9.qKL9 was located in a segment about 1Mb between markers D7 and N23 using progeny tests of BC4F2 and BC5F1 in the spring of 2015.The alleles derived from the large kernel parent V671 play a role in increasing kernel length.At the same time,we found a new QTL with an influence on grain length that was namedqKL9-2 which was identified in the region about 27 Mb between markers 9-43 and L32,and alleles derived from the small kernel parent Mc were synergistic.The results showed that the original QTL were genetically decomposed into two major QTLs,qKL9 and qKL9-2.4.Authenticity verification ofqKL9 and qKL9-2.Progeny tests were carried out using pure lines which span and overlap with each other in the target segment,and the qKL9 was fine-mapped between markersD7 and N23,and qKL9-2 was located between markers 9-43 and L32 again based on phenotype of kernel length in one year under three environmental conditions,qKL9-2 was located between markers 9-43 and L32 based on phenotype of kernel width and hundred-kernel weight all the same.These results fully confirmed that the two main QTLs qKL9 and qKL9-2waretrue and reliable,and provided guarantee for further fine mapping and gene cloning.5.Candidate gene prediction in qKL9 target segment.According to the reference genome of maize V2,there were 21 candidate genes in the physical distance of about 1 Mb between marker D7 and N23.Among them,The GRMZM2G025812 and GRMZM2G704285 genes were found to have differential expression by more than 2 times in the two parents V671 and Mc,and GRMZM2G025812 was detected to have differential expression both in9 DAP and 14 DAP based on the result ofRNA-sequencing of 9DAP and 14 DAP after pollination.GRMZM2G025812 had high expression in seeds by bioinformatics analysis.The homologous gene of which in rice is Os06g0622700,which involved in the activation of expression of the chaperone gene BiP gene that affect the endosperm structure,seed phenotype and grain weight.So it was speculated as a key candidate gene for controlling kernel length.