亞洲綠豆品系根系結構的遺傳定位

Abstract

各種環境變化造成的選拔壓力，都能夠促使植物改變性狀。經過長時間的篩選，不同地區的族群會產生遺傳差異，導致對非原棲地的適應性下降，也就是所謂的地區適應 (local adaptation)。當以任何方式抵達新的棲地，氣候條件的變化對植物來說就是一種逆境。而植物對逆境的反應可分為三種：逃避 (escape)、迴避 (avoidance)，以及忍受 (tolerance)。在乾旱適應方面，發展根系是植物經常利用的策略之一。綠豆在亞洲是常見的豆科作物，具有豐富的營養價值。在前人研究中推測，綠豆的擴散是由馴化中心南亞，以逆時針的方向傳至東南亞、東亞，最後抵達中亞地區，其背後的原因可能與降水量和農民種植習慣相關。研究中也發現四個綠豆族群 (南亞、東南亞、東亞、中亞) 之間存在顯著的遺傳差異，影響到根莖比 (root:shoot ratio)。然而，綠豆根系結構如何受到環境選拔，以及其遺傳結構的變化如何影響根系發展需要進一步研究。本篇研究利用水耕系統種植 224 個綠豆品系，並測量 14 個根部型態性狀與 6 個根部重量相關性狀。結果顯示，東南亞族群的根系結構和植株重量顯著高於其他族群，而中亞族群的根莖比顯著高於其他族群。透過全基因體關聯性分析(Genome-Wide Association Study)，我們找到 3 個基因與根部型態相關，1 個基因與根莖比相關。我們挑選在全基因體關聯性分析中顯著的基因座 (locus)，記錄最顯著位點的基因型 (genotype) 並比較各個等位基因 (allele) 的性狀表現。結果與我們觀察到的性狀差異相符，東南亞族群與中亞族群分別在根部型態相關性狀與根莖比擁有較多增加性狀的等位基因 (trait-increasing allele)。另外，本篇研究使用預測的氣候因子探討根部型態與氣候的關聯性。結果顯示，這些氣候因子能夠連結到真實的地理區域，並且符合各族群對應區域的氣候型態。本篇研究為環境變化驅使綠豆根系型態適應環境提供新的見解。

Environmental changes shape the phenotypes of plants. Over time, the population’s fitness in its original habitat is higher than in other environments, a phenomenon known as local adaptation. When plants are brought to new surroundings, climatic differences act as a stress. To confront stresses, plants have evolved three strategies: escape, avoidance, and tolerance. The root development is a common strategy for plants to cope with drought stress. Mungbean is a nutrient-rich legume widely cultivated across Asia. In a previous study, mungbean spread in a counterclockwise direction, from South Asia to Southeast Asia, East Asia, and finally Central Asia. This route may be influenced by the difference in precipitation and farming practices. Furthermore, the study classified four genetic groups (South Asia, Southeast Asia, East Asia, and Central Asia) exhibiting two morphologies: one characterized by larger plant size and the other by a higher root:shoot ratio. However, the genetic structure of mungbean for the adaptation to different environments remains unclear. In this study, we obtained 14 root morphological and six weight-associated traits using a hydroponic system. The Southeast Asia accessions had a larger root structure and higher plant weight, while the Central Asia accessions had a higher root:shoot ratio. Through Genome-Wide Association Study (GWAS), we identified three genes associated with root morphologies and one gene associated with root:shoot ratio. We counted the trait-increasing allele in every accession, and the result aligned with our observation on traits. Additionally, the predicted climate variables could link the genetic groups with actual geographic regions. This study provides insight into how different environments drive the adaptation of mungbean root architecture.