QTL Mapping Of Photoperiod Sensitivity Related Traits And Transcriptome Analysis In Maize

Maize is a cereal crop that originated in the tropics.Tropical maize is rich in germplasm diversity and contains a large number of excellent genes that are not found in temperate maize,which is a high quality material for expanding and innovating maize germplasm.Most tropical maize plants in temperate regions have severe photoperiod response,which hindrates the utilization of tropical germplasm resources.Therefore,it is of great significance to further understand the genetic rules of photoperiod sensitivity of maize and identify related genes for the expansion of germplasm resources and variety improvement in China.In this study,recombinant inbred lines derived from maize inbred line LDC-1（photoperiod-sensitive type）and inbred line YS501（photoperiod-insensitive type）were used as materials.Combined with high-density genetic linkage map,QTLs related to photoperiod-sensitive traits were mapped to explore QTLs that can be stably expressed under multiple environmental conditions.The chromosome fragment substitution line and residual heterozygous line constructed by the above inbred lines were used as materials to verify and fine map one of the key QTL.On this basis,the near isogenic lines were used for transcriptome analysis,and the candidate genes of key QTL and the regulatory pathways involved were explored.The main results are as follows:1、Preliminary mapping of photoperiod QTLs.The flowering-related traits of RIL population at days to tasseling,days to pollen-shedding and days to silking were investigated in two long-day environments（Xinjiang 2020 and Xinjiang 2021）and three short-day environments（Yangzhou 2020,Hainan 2020 and Zhenjiang 2020）.Two methods were used to locate QTLs for photoperiod:（1）In five environments,106 flowering-related QTLs were detected,and the positions of flowering-related QTLs on chromosomes in long and short days were compared,and six QTLs controlling photoperiod were found.Based on the best linear unbiasedness property（BLUP）values of flowering traits in two environments,photoperiod sensitivity coefficients were calculated,and 13 QTLs controlling photoperiod were identified.There were four photoperiod QTLs detected by both methods,namely qPR3,qPR8,qPR9 and qPR10,respectively.Among them,qPR8 and qPR10 candidate genes have been cloned,candidate genes are photoperiod genes ZCN8 and ZmCCT10,qPR3and qPR9 are new photoperiod QTL.The phenotypic contribution rates of qPR9 and qPR3 were 5.67%18.01%and 2.55%-6.38%,Respectively,qPR3 and qPR9 was expressed in the longday environment and short-day environment.2、The verification and fine positioning of qPR9.Four remaining heterozygous heterozygous lines with qPR9 segment hybridization were selected from the chromosome fragment substitution lines constructed with LDC-1 as the donor and YS501 as the acceptor,and their self-bred offsprings were planted into plots under short sunshine conditions.According to the flowering differences among different genotypes in the plot,the qPR9 interval was reduced to 57.69 Mb.Twelve fragment substitution lines carrying donor fragments in the target region of qPR9 were selected from the chromosome fragment substitution lines.According to the flowering time difference between the 12 fragment substitution lines and the recipient parents under short-day conditions,the qPR9 interval was reduced to 26.92 Mb.By finding the overlapping interval of the two positioning methods,the qPR9 interval is finally reduced to 19.61 Mb.3、Transcriptome analysis.Using qPR9 near-isogenic lines qPR9-NILLDC-1 and qPR9-NILYS501 as materials,transcriptome sequencing was performed at V4 stage under short-day treatment.Compared with qPR9-NILYS501,there were 1585 differentially expressed genes in qPR9-NILLDC-1,of which 973 genes were up-regulated and 612 genes were down-regulated.GO enrichment analysis of 1585 differentially expressed genes showed that the most enriched Term was photosynthesis and light capture of light system Ⅰ.The KEGG enrichment analysis showed that the pathways of obvious enrichment were photosynthetic antenna protein,carotenoid biosynthesis,and cholesterol biosynthesis.The above results show that qPR9 may lead to significant differences in the expression of genes related to photosynthetic activity,partial pigmentation and hormone synthesis between near-isogenic genes.The location analysis of 1585 differentially expressed genes showed that 7 genes were located in the qPR9 candidate region.Combined with bioinformatics analysis and gene expression analysis,it was preliminarily speculated that one of the genes homologous to Arabidopsis COL9 was qPR9 candidate gene.