G.41×新疆野苹果树体生长性状的QTL精细定位及候选基因预测

QTL Fine Mapping and Candidate Gene Prediction for Growth Traits in G.41×Malus sieversii

【目的】矮化砧木可以诱导地上部接穗品种矮化,实现苹果的丰产和稳产。因此,深入挖掘调控苹果树体生长的基因,可以改善苹果树形,加强苹果园地的管理方便性。【方法】以矮化苹果砧木‘G.41’和乔化苹果砧木新疆野苹果(Malus sieversii)为亲本构建的188株F1代分离群体为试材,并于每个分离群体植株上嫁接‘富士冠军’。基于SSR标记技术,采用Join Map 4.0作图软件构建苹果遗传连锁图,应用Map QTL 5.0作图软件,结合后代群体的表型数据,对接穗高度和接穗横截面积生长性状进行初步QTL定位。结合苹果基因组序列信息,利用Primer5.0软件进行新SSR标记开发,并对初步定位区域进行精细定位及候选基因预测。【结果】该研究从361对SSR引物中筛选出108对在亲本之间表现出多态的SSR引物,多态率为29.9%。其中95对引物用于遗传连锁图谱构建,并在5号连锁群上初步检测出4个与植株生长性状相关的QTL位点,与接穗高度、接穗横截面积性状紧密连锁的两个标记,为L05024和Hi09b04。根据初步定位区域的序列信息,设计了新的SSR引物24对,其中在亲本间表现出多态的有10对,利用该10对引物对5号连锁群重新分析。构建了包含21个SSR标记、总长为86.0 c M的高密度遗传图谱,其平均遗传距离为7.52 c M。通过对接穗高度与接穗横截面积生长相关性状的QTL分析,在SSR标记L05024和Hi09b04之间找到与其相关的QTL位点,其表型贡献率分别为19.2%和51.7%。将该QTL位点与基因组序列对比,发现其物理距离为543 kb,并且该QTL区间包含16个候选基因。推测其中MDP0000323212为与植株生长密切相关的基因。【结论】本研究将砧木诱导矮化基因定位于苹果第5号染色体543 kb区段内,侧翼标记分别为L05024和Hi09b04,其物理距离为4.048—4.591 Mb,并筛选到可能参与调控植株生长的候选基因MDP0000323212。

【Objective】Dwarf rootstock is an important germplasm to be utilized in the production of high and stable yields of apples by inducing dwarf scions. Mapping the genes that regulate the growth of apple trees has important theoretical and practical significance for improving apple＇s yield and quality. 【Method】 In this study, 188 F1 progenies derived from the cross G.41×Malus sieversii were used to perform QTL mapping, and ‘Fuji Champion＇ were grafted on every F1 plant. Subsequently, based on SSR markers, a genetic map of apple was constructed using Join Map 4.0 software. Using Map QTL 5.0 mapping software, the growth traits, including scion height and cross-sectional area of the scion were used as phenotypic data in QTL preliminary analysis. Combined with information from the apple genome sequence and newly developed SSR markers using Primer 5.0 software, the QTL has been defined and the candidate genes were predicted. 【Result】 In this study, a total of 108 out of 361 SSRs showed a variable degree of polymorphism, and the polymorphism rate was 29.9%. A genetic map was constructed using 95 of 108 polymorphism SSRs and four QTLs for the growth trait were detected in linkage group No.5. Two markers（L05024 and Hi09 b04） were closely linked with the height and the cross-sectional area of scion. Combined with the genome sequence, 24 new SSR markers were developed, which contained 10 polymorphism markers. Subsequently, the linkage group No.5 was analyzed again using these 10 markers. The reconstructed high density linkage group, consisted of 21 SSR markers, spanning 86.0 c M with an average of 7.52 c M per marker. The QTLs responsible for the height and the cross-sectional area of the scion were defined and two relevant SSR markers（L05024 and Hi09 b04） were identified accounting for 19.2% and 51.7% of the observed phenotypic variation. According to the ‘Gold Delicious＇ genome sequence, this locus has been defined in a region of 543 kb that contains 16 candidate genes and a gene（MDP0000323212） was considered as the candidate gene for plant growth in this QTL interval. 【Conclusion】 In this study, genes responsible for dwarfing were located in a 4.048-4.591 Mb interval on apple chromosome No.5 and two high linked SSR markers（L05024 and Hi09 b04） were identified. A gene（MDP0000323212） was identified as a potential candidate gene for growth traits.