Mining Candidate Genes For The First Effective Branch Number In Brassica Napus

Brassica napus L.is one of the most widely grown oil crops in the world,and increasing the yield of rapeseed is an important goal of breeding.The first effective branch number is one of the important agronomic traits of B napus.Many studies have shown that increasing the first effective branch number of B napus can effectively improve its yield.The first effective branch number trait of rapeseed is a typical quantitative trait,and its genetic mechanism is relatively complex.The genetic and regulation rules of this trait are still unclear,and the genetic resources that can be used for genetic improvement of this trait are still limited.Therefore,further exploration of candidate genes for the first effective branch number trait of B napus.can lay a foundation for high-yield breeding of B napus.In this study,inbred lines with more and less primary effective branches were selected from 200 inbred lines of B napus.from different sources to construct F₂ segregating population,and genetic mapping of the traits of primary effective branches in this population was carried out;In combination with RNA sequencing（RNA-seq）,microstructure observation,and hormone content determination of shoot apical meristems at seedling stage,preliminary Analyze the complex genetic mechanism of the first effective branch number trait in B napus.,reveal the cytological regularity and hormone content characteristics of the first effective branch formation,and discover candidate genes for the first effective branch number trait in B napus..In order to provide a basis for the genetic improvement of rapeseed multi-branch.The main results of this study are as follows:1.The F₂ segregating population was constructed by using the multi-branched inbred line 19C080 and the less-branched inbred line 19C076,and based on resequencing,the bulk segregant analysis（BSA）was used to locate 4 quantitative trait locus（QTL）,located on chromosomes C02（2）,A02（1）and C08（1）,respectively,and there are a total of 1023 genes in these four candidate regions.2.Select the multi-branched 20Z141,19C080,19C159 and the less-branched19C064,19C076,20Z130 from the natural population,and perform RNA-seq on the shoot apical meristem of the 6 materials at the seedling stage.The results showed that the numbers of differentially expressed genes in the three comparison groups of19C064vs20Z141,19C076vs19C080 and 20Z130vs19C159 were 10165,6629 and9307,respectively,and there were 809 differentially expressed genes in the three comparison groups.GO enrichment analysis found that most of the differentially expressed genes were enriched in GO term related to enzyme activity;KEGG enrichment analysis found that most of the differentially expressed genes were enriched in the metabolic pathways of synthesis and degradation of secondary metabolites;Many differentially expressed genes were found to be hormone-related.3.The content of endogenous hormones in the shoot apical meristems of the parent materials 19C080 and 19C076 at the seedling stage of the first effective branch number segregation population was determined,and it was found that the content of Zeatin（Zeatin=TZ+CZ+DZ）and trans-Zeatin in the shoot apical meristems of19C080 seedling stage was significantly higher than that of 19C076,and the content of trans-Zeatin riboside and dihydrozeatin riboside in the shoot apical meristems of19C080 seedling stage was significantly higher than that of 19C076,and the content of cis-Zeatin in 19C080 seedlings;the content in the shoot apical meristems of19C080 was significantly lower than that of 19C076,and the content of isopentenyladenosine in shoot apical meristems of 19C080 was significantly lower than that of 19C076;The content of GA₃ in gibberellin was significantly higher than that of 19C076 at the shoot apical meristems of 19C080,while the content of GA₄ in the shoot apical meristems of 19C076 was significantly higher than that of 19C080;The contents of other hormones including auxin,abscisic acid,brassinolide and strigolactone were not significantly different in the multi-branched and less-branched materials.4.Microstructural observation of the shoot apical meristems and axillary buds of multi-branched 20Z141,19C080,19C159 and less-branched 19C064,19C076,20Z130 at seedling stage showed that shoot apical meristems of multi-branched and less-branched materials were found at seedling stage.The morphology and degree of differentiation of tissues and axillary buds were different.The multi-branched materials had more axillary buds and the axillary buds differentiated faster than the less-branched materials.In addition,the material transportation system of multi branched materials was more developed.5.A total of 105 candidate genes were screened by combining BSA-seq and RNA-seq,30 on chromosome A02,56 on chromosome C02 and 19 on chromosome C08.There are 7 transcription factors among these candidate genes,and the functions of a small number of genes are not annotated.These screened candidate genes laid a solid foundation for follow-up research and high-yield breeding and improvement of rapeseed.