厚皮甜瓜心部果肉蔗糖含量QTL定位及候选基因分析

QTL Mapping and Candidate Gene Analysis of Sucrose Content in the Center Flesh of Muskmelon

【目的】运用QTL分析厚皮甜瓜心部果肉蔗糖含量,挖掘影响该性状的候选基因,为厚皮甜瓜甜味性状的遗传改良奠定理论基础。【方法】以高糖材料VZX(V醉仙)为母本和低糖材料HP(高代自交系)为父本杂交衍生的F_(2)群体为研究对象,利用高效液相色谱仪测定果实赤道位置心部果肉蔗糖含量,从F_(2)群体中挑选蔗糖含量极端高和极端低的单株各20个,分别构建高蔗糖池和低蔗糖池,对双亲及混合池均进行全基因组重测序(约20×覆盖深度),定位蔗糖性状的关联区间,并结合生物信息学分析候选基因。【结果】厚皮甜瓜心部果肉蔗糖含量在F_(2)群体中基本呈正态分布,符合典型的数量性状遗传特征;对双亲及混池进行全基因组重测序,共获得有效数据32.62 G,Q20在95%以上,平均覆盖深度为17.76,比对到参考基因组上的总reads数目比例在98.72%~99.02%,测序数据质量高,参考基因组选择合理有效;在8号染色体定位到1个3.29 Mb的区间,共注释到108个基因;在初定位区间内获得1个参与糖酵解和糖异生生化过程的候选基因EVM0000647,在高糖和低糖亲本间编码区无非同义突变,但启动子区域具有大量差异位点,且表达量具有明显差异。【结论】极端混池测序(BSA)方法,在8号染色体上定位到1个影响厚皮甜瓜心部果肉蔗糖含量的QTL,大小为3.29 Mb,共注释到108个基因,其中候选基因EVM0000647,通过差异表达负调控厚皮甜瓜心部果肉蔗糖的积累。

【Objective】This project aims to analyze the content of sucrose in the center flesh of muskmelon by QTL mapping and find out the candidate genes,thus laying a genetic foundation for the genetic improvement of muskmelon with high sucrose content.【Method】The F_(2) population was derived from a cross between VZX with high sucrose content as the female parent and HP(high generation inbred lines)with low sucrose content as the male parent.The sucrose content determination was based on high performance liquid chromatography(HPLC).QTL for the sucrose content in the center flesh of muskmelon were detected by bulked segregant analysis(BSA)method and candidate genes were analyzed combined with bioinformatics.【Results】The sucrose content in the center flesh of muskmelon was approximately normal distribution in the F_(2) population,which was consistent with the genetic characteristics of quantitative traits.A total of 32.62 G(average 8.16 G)of valid data were obtained by whole-genome resequencing of the parents and two bulked pools,and a 3.29 Mb interval was located on chromosome 8.A total of 108 genes were annotated.After that,further GO enrichment analysis and KEGG pathway analysis were carried out.A candidate gene EVM0000647 involved in glycolysis and gluconeogenesis in the initial localization interval was obtained by combining transcription data.There were no synonymous mutations in the coding region of EVM0000647 between the high-glucose and low-glucose parents,but there were a lot of different sites in its promoter region,and the expression levels were obviously different between parents.【Conclusion】One QTL with 3.29 Mb interval is located on chromosome 8 based on BSA method.EVM0000647 gene involved in glycolysis and gluconeogenesis pathway is identified by bioinformatics analysis.There are distinct differences in the expression levels between high-glucose and low-glucose parents,which may play a significant role in the sucrose accumulation in the center flesh of muskmelon.