全基因體關聯性分析尋找黃果蠅諾麗果毒性耐受基因

Abstract

食性的適應在物種分化的過程中扮演重要的角色，但是我們對於在食性適應的早期，生物在遺傳上有什麼樣的改變還不甚了解。在果蠅食性適應的例子中，有些果蠅能夠去取食諾麗果這種對於大部分的果蠅物種都有毒的食物，例如塞席爾果蠅。本研究利用了黃果蠅這種目前已知在不同品系之間有對於諾麗果毒素存在耐受性差異的物種，去了解食性適應之前有什麼樣的基因參與了諾麗果毒素的解毒。總共117個來自北美的黃果蠅品系參與了全基因體關聯性分析，我們發現到不同性別以及品系間都存在著諾麗果毒素耐受性的差異。在將近四百萬個遺傳變異中有116個在不同性別中都被發現和諾麗果毒素耐受性有相關，而這些遺傳變異大多座落於非編碼區。在和塞席爾果蠅及其他近源種果蠅相比較之後發現，大部分的遺傳變異只出現在黃果蠅中，而且是在種內既有的遺傳變異。我們更近一步的利用這些遺傳變異去預測非洲族群的黃果蠅對於諾麗果毒素的耐受性並且和真實的耐受性比較之後，讓我們了解到非洲族群和北美的族群可能存在著不同的機制參與諾麗果毒素的解毒。這些發現讓我們更了解在生物食性適應的早期在遺傳上有什麼變化。

Diet adaptation is an important cause of host-associated differentiation. Many studies have focused on the species in which host specialization has driven speciation or population differentiation. However, it is still unknown the underlying genetic changes evolved earlier during specialization. In Drosophila, noni fruit is toxic to most species except very few species such as D. sechellia. Multiple mechanisms have been involved in the noni specialization in D. sechellia. To understand early genetic changes during diet adaptation, we chose D. melanogaster that exhibits some tolerance variation to noni fruit. We performed a genome-wide association study (GWAS) to reveal the genetic basis of noni-toxin tolerance in D. melanogaster using 117 DGRP (Drosophila Genetic Reference Panel) lines. We found considerable sexual and strain variation of noni-toxin tolerance. Among the ~4 million variants detected in the 117 DGRP lines, 116 candidate variants shared between the two sexes were associated with the noni-toxin tolerance. These candidate variants were mainly located in non-coding regions of the genome. The genetic basis of toxin tolerance in D. melanogaster is different from that in D. sechellia because most candidate variants were derived alleles, which were not present in the closely related species including D. sechellia. These candidate variants were mainly coming from standing variation, which also exists in ancestral African populations. The correction between these candidate variants identified from the American DGRP population and the observed noni-fruit tolerance in the two African DPGP2 populations, suggesting that the underlying genetic bases of tolerance are different. These findings advance our understanding of the underlying genetic change of early evolution in diet adaptation.