谷子苗期耐低氮相关性状的QTL分析

QTL Analysis for Seeding Traits Related to Low Nitrogen Tolerance in Foxtail Millet

【目的】分析谷子(Setaria italica L.)耐低氮性状相关的QTL,为耐低氮基因的精细定位、克隆及功能研究奠定基础,同时,也为揭示谷子耐低氮遗传机理和培育耐低氮谷子品种提供技术支撑。【方法】以耐低氮品种豫谷28和低氮敏感品种七叶黄为亲本构建的包含120个家系的重组自交系(RIL)群体为试验材料,在谷子苗期进行低氮和正常氮处理,并对处理21 d的水培幼苗的苗长、主根长、根干质量、苗干质量、总干质量、叶绿素相对含量、植株含氮量7个性状进行分析。同时,采用复合区间作图法(composite interval mapping,CIM)对耐低氮相关性状进行QTL定位与分析,并对QTL置信区间内的候选基因进行预测。【结果】在低氮和正常氮水平下,RIL群体的耐低氮相关性状均表现为连续正态分布,且呈双向超亲分离现象,符合典型的数量性状遗传特点,适于QTL分析。相关分析表明,苗长与主根长、根干质量、苗干质量、总干质量、叶绿素相对含量呈极显著正相关,主根长与植株含氮量呈显著负相关。共定位到低氮和正常氮水平下与苗长、主根长、根干质量、苗干质量、总干质量、叶绿素相对含量及植株含氮量相关的34个QTL,分布于第1—9染色体,单个QTL表型贡献率为5.15%—52.42%。其中,2种氮水平下共同定位到10个QTL,低氮和正常氮单一环境下分别定位到11和13个QTL。15个为主效QTL,qRDW3、qMRL1.1、qMRL1.2、qSL5和qSPAD15个主效QTL在2种氮水平下均被定位到。共检测到5个QTL重叠区,聚集了2种氮水平下多个性状的QTL,通过基因预测与功能注释,筛选出5个QTL置信区间内6个与氮代谢相关的候选基因,表明氮同化、吸收和利用相关基因极有可能控制了这些基因的表达。【结论】34个QTL分别聚集于9条染色体上的16个QTL簇,基于基因注释,共筛选了6个与谷子氮代谢相关的候选基因,表明不同性状参与到了共同遗传机制,并可通过分子标记辅助选择进行耐低氮有利等位基因的聚合育种。

【Objective】The analysis of quantitative trait loci(QTL)related to low nitrogen tolerance traits of millet(Setaria italica L.)laid a foundation for fine mapping,cloning and functional research of low nitrogen tolerance genes.At the same time,it also provided technical support for revealing the genetic mechanism of low nitrogen tolerance of millet and breeding low nitrogen tolerance varieties.【Method】The recombinant inbred line(RIL)population consisting of 120 family lines was used as experimental materials,that was constructed from parents Yugu 28,a low nitrogen tolerant variety,and Qiyehuang,a low nitrogen sensitive variety.The RIL populations were treated with low nitrogen and normal nitrogen at seedling stage,and seven traits were analyzed of hydroponic for 21 days,which inculding seedling length,maximum root length,root dry weight,seedling dry weight,plant dry weight,relative chlorophyll content and plant nitrogen content.At the same time,we used composite interval mapping(CIM)to locate and analyze QTLs for traits related to low nitrogen tolerance,and predicted the candidate genes in the confidence intervals of QTLS.【Result】The traits associated with low nitrogen tolerance of RIL populations exhibited continuous distribution with apparent transgressive segregation both under low nitrogen and normal nitrogen levels,which conformed to the typical genetic characteristics of quantitative traits and were suitable for QTL genetic analysis.Correlation analysis showed that seeding length was positively correlated with maximum root length,root dry weight,seeding dry weight,plant dry weight and relative chlorophyll content,and maximum root length was negatively correlated with plant nitrogen content.A total of thirty-four QTLs related to seeding length,maximum root length,root dry weight,seeding dry weight,plant dry weight,relative chlorophyll content and plant nitrogen content were located under low nitrogen and normal nitrogen levels,which distributed on chromosomes from 1 to 9.They explained individually 5.15%-52.42%phenotypic variation.Ten QTLs were simultaneously detected under both two nitrogen levels,eleven and thirteen QTLs were only identified under single low nitrogen and normal nitrogen conditions,respectively.A total of fifteen QTLs were major QTL,and five major QTLs were repeatedly detected under both two nitrogen levels,which including qRDW3,qMRL1.1,qMRL1.2,qSL5 and qSPAD1.Five QTL overlaps were detected with gathering multiple QTLs under two nitrogen levels.Six candidate genes related to nitrogen metabolism were identified from the confidence interval of the five QTL overlaps,suggesting that genes related to nitrogen assimilation,absorption and utilization probably control the expression of these genes.【Conclusion】Thirty-four QTLs were scattered on sixteen clusters of nine chromosomes.Based on gene annotation,a total of 6 candidate genes related to nitrogen metabolism were screened in foxtail millet,indicating the different traits involved in common genetic mechanisms,and the favorable alleles for low nitrogen tolerance can be polymerized by marker-assisted selection.