從阿拉伯芥不同族群之性狀差異探討雜草演化

Abstract

雜草所具的特徵過去已有許多研究探討過，但關於雜草演化的遺傳機制尚不明瞭。模式物種阿拉伯芥（Arabidopsis thaliana）經先前的研究發現現今分布於南歐半島、非洲的「孑遺族群」過去曾分布於整個歐亞大陸，但雜草般的「非孑遺族群」取代了孑遺族群並散佈至世界各地。儘管對於阿拉伯芥的性狀已有非常多的研究，但過去研究所使用的品系幾乎都來自於非孑遺族群，鮮少有研究探討不同族群間的差異。比較孑遺和非孑遺族群間的性狀差異可使我們能更進一步了解雜草的演化。本研究選了52個來自野外的阿拉伯芥自交品系，其中31個來自非孑遺族群，21個來自孑遺族群，將這些品系種植在相同的環境條件下以比較兩個族群由遺傳造成的性狀差異。研究中主要測量了兩個與雜草有關的性狀：幼苗避陰反應及種子產量。幼苗避陰實驗將阿拉伯芥種子種植在兩個不同光照環境下，比較不同族群在不同光照處理下幼苗下胚軸長度的差異。結果顯示幼苗下胚軸長度在不同處理下有顯著差異，但不同族群間幼苗下胚軸長度以及在不同處理下的可塑性並沒有顯著差異。種子產量的實驗中比較了兩個族群的果實及種子相關性狀。結果顯示不同族群的種子大小及種子產量有顯著差異，孑遺族群的種子大小平均比非孑遺族群的大了33%，但非孑遺族群平均能產出將近孑遺族群兩倍的總種子數。透過FST- QST的比較，我們認為這些存在於孑遺族群和非孑遺族群間的性狀差異很可能是天擇推動造成的。種子產量的差異使阿拉伯芥非孑遺族群很可能有著比孑遺族群高的適存度，使其能取代孑遺族群並廣泛散佈。此研究結果未來可進一步利用數量表徵基因座定位法及全基因組關聯分析找出控制阿拉伯芥非孑遺族群成為雜草的候選基因，以了解雜草演化的遺傳機制。

The characteristics of weedy plants have been studied for a long time, but the genetics of weedy plant evolution remains unclear. Previous researches showed that the model plant Arabidopsis thaliana consists of multiple genetic groups. The “relict” populations currently found in Southern Europe and Africa once occupied most of Eurasia, but the weedy “non-relict” population rapidly replaced the relict populations and spread worldwide. While many traits of A. thaliana have been much studied, most laboratory strains were from non-relict populations, and few studies have investigated the differences between relicts and non-relicts. Comparing the phenotypic variances between these two groups provides a way to study the genetics of weedy plant evolution. Fifty-two accessions of A. thaliana were used in this study, including 31 non-relict and 21 relict accessions. All accessions were grown in controlled conditions to compare their phenotypic differences. Two types of traits associated with weediness were measured: shade avoidance response and seed productivity. For shade avoidance response, we treated the seedlings with two different light conditions. The hypocotyl length of seedlings showed significant differences between treatments but not between populations. For seed- and fruit-related traits, we observed significant differences for seed size and productivity: Seeds from relicts were about 33% bigger than non-relicts on average, but non-relicts yielded almost twice as many seeds as relicts. According to the results of FST-QST comparison, the phenotypic differences between relicts and non-relicts might be caused by natural selection. Owing to the differences of seed productivity, non-relicts might have higher fitness and spread faster than relicts. This research lay a foundation for further quantitative trait loci mapping and genome-wide association study to find candidate genes controlling weedy phenotypes.