Identification Of The Genes Involved In Growth-peroid Regulation And Affected By Enviornmental Factors In Rapeseed(Brassica Napus L.)

Rapeseed(Brassica napus L.)is a major winter crop in China,and as one of the most widely grown oil crops,its advantage of not competing with staple crops for arable land is conducive to the full utilization of land.Flowering time is a crucial developmental stage in the life cycle of rapeseed and influences the yield and quality of seeds.The total growth period of rapeseed varies across ecotypes and genotypes and is influenced by environmental conditions.A lack of knowledge exists about the environmental effects on the regulatory network controlling the growth period of rapeseed.In this study,we conducted an in-depth study on the flowering time-related genes(FTRGs)in the pangenome of rapeseed and their variation across different ecotypes in a genetic population.We planted 292 rapeseed core germplasm accessions that featured rich genetic polymorphisms in six environments and observed their growth-period-related traits.Genome-wide association study(GWAS)on growthperiod traits was conducted using multiple markers,such as single nucleotide polymorphisms(SNPs),genome structural variations(SVs),and presence-absence variation(PAV)of a gene.These results laid a foundation for a better understanding of the regulatory network controlling growth-period traits of the allotetraploid rapeseed,as well as for breeding programs towards an ideal growth-period length.The main results of this study can be summarized as follows:1.Construction of a high-resolution FTRGs variation graphics of rapeseed.A total of 1,337 FTRGs were identified in a pan-genome which was constructed based on 1626 germplasm accessions by referring to the Arabidopsis flowering gene database FLOR-ID.By comparing the FTRGs distribution among various chromosomes and subgenomes,it was found that FTRGs had higher diversity in the A subgenome than in the C subgenome of rapeseed.We compared the frequency differences of FTRGs among different ecotypes in rapeseed,and found 75 FTRGs with significant frequency differences among spring,winter and semi-winter subpopulations.By correlating candidate FTRGs with 14 quantitative trait loci(QTL)known to regulate flowering time,we found that these QTL covered 39 FTRGs.We analyzed and summarized the genetic variation of these genes and identified 6 structral variations(SVs)and 25 FTRGs corresponding to ecotypic differentiation.It was shown that the presence/аbsence vаriаtion(PAV)and structurаl variаtion(SV)of FTRGs could also be effective markers for the selection of ideal flowering time in breeding.2.Observation and analysis of the growth-period traits in different environmentsThe growth-period traits,such as flowering time,silique maturity time and whole growth-period length,were observed and analyzed in the population consisting of 292 core accessions in six environments.At relatively high latitude,where it is cold and dry in winter and of a long day time in spring,the flowering and silique maturity time were delayed,and the total growth-period length was prolonged.The ranking changes of flowering time,silique maturity time and whole growth-period length of an individual accession in the population were observed.A certain accession could have different rank in different environments in respect to their growth-peirod traits.Genetic resources which showed stable performance,mild changes,and drastic changes of growth-period traits across environments were identified,respectively.3.GWAS on growth-period traits in rapeseed using multiple molecular markersThe SNP-GWAS revealed a total of 2961,3112,and 221 candidate genes relating to flowering time,silique maturity time and growth-period length,respectively.The PAV-GWAS discovered a total of 33,33,and 6 candidate genes,respectively.Whereas,the SV-GWAS unveiled a total of 45,35,and 32 SVs,respectively.A different homologous copy was specifically found to an environment.Some genes were found to regulate not only flowering,but also the ripening process of pods.Bna A02G0374400 ZS was significantly correlated with various stages of the whole growth period,and the allelic variations and haplotype difference of Bna A02G0374400 ZS among different ecotypes were further analyzed.Taken together,we identified FTRGs and analyzed their ecotypic differences using the pangenome of Brassica napus.We identified the effects of different environments on the growth-period traits and regulatory genes of different genotypes,and suggested accessions appropriate for multiple environments and for particular environments.GWAS was conducted to identify genes and SVs associated with growth-period traits,and we found that different homologous copies could be associated with growth-period trait variation in different environments,demonstrating the complexity of regulatory networks controlling a certain trait in the tetraploid rapeseed genome.These findings provide a foundation for further research on the genetic mechanism of environmentally biased expression of homologous genes and the reasonable selection of growth-period traits in rapeseed breeding programs.