Molecular dissection of oil content with respect to fatty acid compositions by conditional QTL analysis in oilseed rape

Abstract

Oil content in rapeseed is a complex quantitative trait,which is controlled by multiple genes and influenced by environments.Extensive efforts have been made in mapping of the QTL for this trait since 1995,which indicate that almost all the 19linkage groups have found the presence of oil QTL in Brassica napus.On the other hand,a large body of QTL information for fatty acid compositions is also available because they play an important role in the accumulation of oil content.However,the genetic relationships between oil content and individual fatty acid content on QTL level still remains poorly understood.Our main objective was to evaluate the genetic influence of four major fatty acid components on oil content in a population with no allelic segregation on two major erucic acid gene loci in oilseed rape.In present study,the previously developed doubled haploid(DH)population with Sollux/Gaoyou background(SG-population)was used for QTL identification.Both parents have high seed oil content but also high in erucic acid content.Taking the phenotypic data of oil and the four main fatty acids content from four environments,the new published SG-map was combined to perform the QTL analysis by QTLNetwork 2.0. Results indicated that the additive effects of all mapped QTL showed small but quite significant(P 0.01). The epistatic effects and genotype by environments interaction effects were also small.By unconditional mapping analysis,7,10,10and 5 QTL were identified for erucic acid,oleic acid,linoleic acid and linolenic acid, respectively.Among them,erucic acid QTL on A2,A7,A9and C1,and QTL for oleic acid and linolenic acid in C7 and A9were new identified loci,while five new detected QTL for linoleic acid content were located on A4,A10, C6,C7and C9linkage groups.The numbers of QTL identified in present study for four fatty acid compositions are clearly more than that detected in populations with segregation for erucic acid content,indicating that the existence of allelic differentia in two major erucic acid gene loci might restrain or hide the expression of QTL with minor genetic effects.Conditional QTL mapping indicated that OilA9,OilC2 and OilC8-1 were significantly influenced by linoleic acid,since when oil content was conditioned on linoleic acid,they showed no significant or deeply reduced effects;OilA4 might be influenced by oleic acid,linolenic acid and erucic acid simultaneously,while oleic acid QTL or underling candidate genes may directly contribute to oil content in the loci OilA1,OilA7 and OilC8-2 because QTL for both traits were co-localized and significantly shifted the genetic effects for oil QTL after conditional mapping.In addition,four additional QTL with small effects were only identified in the conditional mapping, further demonstrating the complex genetic inheritance of oil content in B.napus. In conclusion,by comparing unconditional and conditional QTL for oil content,the genetic relationships between oil content and fatty acid compositions on individual QTL were analyzed,which may provide valuable information for breeding varieties with high oil combining high oleic acid content.In the case of no allelic segregation on two major erucic acid gene loci,larger numbers of QTL with significant but small genetic effects were observed for all four major fatty acid compositions.Selection for high erucic acid content based on those flanking markers linked to erucic acid QTL might be special interesting for breeding high erucic acid materials for industry purpose.