鳞砗磲自交家系的近交效应分析

Giant clam is a kind of tropical marine shellfish, mainly inhabit coral reefs. It is hermaphroditic and can self-fertilization or cross fertilization, so they are possible to appear the inbreeding phenomenon during the reproduction process. Our previous experiments showed that the inbreeding ability of the inbred families declined seriously, which laid a good foundation for the study of the inbreeding effect of Tridacna squamosa. In this program, the inbreeding rate and inbred load of phenotypic traits for Tridacna squamosa were analyzed by constructing inbred pedigree and cross family as control. On the basis of genome and transcriptome sequencing, the difference of gene expression between self-bred and hybrid progenies in different growth and development stages was found, and the signal pathway related to inbreeding was screened. 2b-RAD strategy was used to construct the QTL linkage map of inbred families, and to locate the homozygous harmful genes that caused inbreeding decline. The differences between inbred line and hybrid progeny were compared by whole genome re-sequencing method. Genetic mutation, loss of heterozygosity and selective evolutionary association gene were screened in self-bred line relative to hybrid line. The inbreeding decay rate was quantified by FROH and FHOM parameters. Finally, we found common genes as inbreeding recession-related genes by comparing these genes with those mapped by genomic linkage map (QTL),, which revealed the molecular mechanism of inbreeding decline of Tridacna squamosa.

砗磲是一类热带海洋贝类，主要栖息于珊瑚礁中。它雌雄同体，既可以自体受精、也可以异体受精。我们前期实验发现，自交家系存活力产生了严重近交衰退现象，这为研究砗磲近交效应奠定了良好的基础。本项目拟通过构建砗磲自交家系，以杂交家系为对照，分析砗磲表型性状的近交衰退率及近交负荷；针对典型的生物学性状，以基因组为基础，通过转录组测序，找到不同生长发育阶段自交与杂交子代的基因表达差异，从而筛选到与近交衰退的相关信号通路；采用2b-RAD策略构建自交家系的QTL遗传连锁图谱，定位引发近交衰退的纯合有害基因；采用全基因组重测序方法比较自交系与杂交系子代组间差异，筛查出自交系相对于杂交系的遗传突变、杂合性缺失、及选择性进化关联基因，利用FROH及FHOM参数量化近交衰退率。最后，把这些基因与基因组连锁图谱QTL定位出的基因再次比对，找到共有基因作为近交衰退相关基因，揭示鳞砗磲近交衰退的分子机制。

砗磲是一类热带海洋贝类，主要栖息于珊瑚礁中。它雌雄同体，既可以自体受精、也可以异体受精。此前实验发现，自交家系存活力产生了严重近交衰退现象，这为研究砗磲近交效应奠定了良好的基础。本项目中，我们建立了无鳞砗磲、鳞砗磲、番红砗磲的自交家系和杂交家系，测试了3种砗磲在生活史中的近交衰退率。结果表明：近交衰退现象主要发生在变态期间，对其变态率造成了显著影响。在3种砗磲中，大型砗磲尚未受到变态影响，但对于中小型砗磲造成了严重响应。这对于我们今后开展砗磲苗种繁育提供了良好的策略，在此基础上，我们开展了砗磲品系间、群体间、种间杂交研究，发现随着遗传距离增大杂种优势增加，但是属间杂交尚未产生杂种优势。值得一提的是，通过种间杂交可以获得贝壳形态与外套膜颜色互换的新品系，这为良种创制提供了技术保障。此外，我们还对其性腺发育中的FOXL2基因进行了克隆定量表达研究，发现该基因是雌性为主导的1个基因，也发现了维持雌雄同的一些基因，这为解析生殖机理提供了基础。