基于连锁和关联分析剖析甜瓜幼苗耐冷性的遗传基础

Melon, a typical non-cold-acclimation plant, is sensitive to low temperature. At the stage of seedling raising and the primary stage of transplantation into the field, the melon seedlings are often suffered from chilling injury. Deep understanding of the genetic basis of chilling resistance in melon, discovery of the chilling-resistance genes using modern molecular biotechnologies, and development of new cultivars with improved chilling resistance, are useful approaches to overcome the chilling injury at seedling stage and produce high-yield and -quality melon fruits. Previously, our laboratory developed a melon core collection, which revealed a wide variation in chilling resistance, and from them, we identified a thin-skin accession “Hamasu-5” with a strong chilling resistance. The further research showed that “Hamasu-5” contained the major genes conferring chilling resistance. The F2:3 family population, which derived from a cross between chilling-resistance and chilling-sensitive accessions, and a core collection with additional germplasms are used as materials in the present research. The reduced-representation genome sequencing (RAD-seq) technology is used for genotyping of the melon accessions. The linkage and association analysis are applied to fine mapping of the major QTLs for chilling-resistance in melon seedlings and further explore the genes and function loci that affect the phenotypic variation. Also, the practicable molecular markers will be developed from the QTLs, which will act as a useful tool in molecular breeding. Our results are expected to enhance our understanding of the genetic basis of chilling resistance variation in melon seedlings and construct the platform of materials, technologies and gene resources for melon molecular breeding.

甜瓜是典型的非冷驯化植物，对低温敏感，生产中育苗及定植初期常常遭受低温冷害的侵袭。深入理解甜瓜耐冷性的遗传基础，挖掘耐冷相关基因，培育强耐冷的品种，是克服苗期冷害、生产优质高产甜瓜的有效途径。本实验室前期构建了一个甜瓜核心种质，其耐冷性变异广泛，并从中鉴定了一个强耐冷的薄皮种质“蛤蟆酥-5”。进一步的研究表明，该种质中存在耐冷的主基因。本研究拟以耐冷和冷敏的材料构建F2:3群体，同时以甜瓜核心及附加种质为关联群体，采用高通量RAD-seq技术进行基因分型，联合连锁和关联分析方法精细定位幼苗耐冷性主效QTL，深入挖掘影响表型变异的基因和功能位点，并开发适用性分子标记。研究结果预期能帮助明确甜瓜幼苗耐冷性变异的遗传基础，为甜瓜分子育种积累材料平台、技术平台和基因资源。

本项目对甜瓜幼苗耐冷性进行综合评价，在此基础上结合全基因组关联分析和连锁分析对甜瓜苗期耐冷性QTL进行定位，并发掘变异位点及相关基因。采用SSR和CAPS标记对甜瓜自然群体（核心种质及附加种质）进行基因型鉴定，结果发现自然群体可分为2大亚群，分别对应厚皮melo和薄皮agrestis两个亚种。采用一般线性模型，在自然群体中检测到51个耐冷性相关位点，共74次性状标记关联，其中整个自然群体中共有35个，厚皮种质和薄皮种质中分别有21个和18个，两类种质的共享位点8个。CMCT505_Chr.1在不同种质和不同环境条件下重复出现，可能是一个主效QTL。针对稳定出现的关联位点，从中鉴定了11个有利自然变异。构建了一个包含261个F2:3家系的群体，其第一片真叶冷害指数（CIIF）和第一、二片真叶冷害指数（CIIT）均符合正态分布，对对优选的140个F2单株进行简化基因组测序，构建了一张包括3859个SNP、长度1403.59 Mb的遗传图谱，采用SSR标记对图谱的gap进行加密，采用区间作图法在第3、6、8染色体上检测到4个控制甜瓜苗期冷害的QTL，表型变异解释率在8.88%-11.32%之间，3个QTL的加性和显性效应为负值，可以降低幼苗的冷害程度。进一步将分析这些QTL的候选基因及其功能，将为甜瓜耐冷性分子改良奠定基础。本项目发表SCI论文2篇，核心期刊论文1篇，申请专利1项，国内作学术报告2次，培养研究生3人。