植物是固著性生物，無法自行選擇生長的環境，所以研究植物如何抵抗逆境是一門很重要的課題。高溫及水份逆境是兩種主要影響植物生長與發育的因子，也經常同時發生，顯示出植物對這兩種逆境的反應及基因的表現有程度上的關連性。之前的研究已知，阿拉伯芥hit1突變株喪失了對高溫及水份逆境的正常耐受性。為了找出造成此性狀的遺傳因子，進而探索植物在面對此兩種逆境時的反應，本研究遂利用基因定位的方式，標定出突變點位於登錄序號At1g50500之基因上。將阿拉伯芥野生型HIT1基因轉殖至hit1突變株後可將突變株之性狀恢復為野生型，確認了HIT1基因影響阿拉伯芥抵抗高溫及水份逆境的角色。HIT1基因經過轉譯，可得一帶有到829個胺基酸之蛋白質，序列比對之結果顯示其與酵母菌Vps53p蛋白質有最高的相似度。Vps53p蛋白質在酵母菌中扮演著繫栓因子(tethering factor)的角色，與Vps52p及Vps54p共構成聚合體，參與將微粒體(vesicles)運往late Golgi的工作。酵母菌若喪失Vps53p，其生長速率在37度C的高溫下會比野生型緩慢許多。該下降之生長速率可藉由阿拉伯芥HIT1基因之殖入而得部份之補償，顯示阿拉伯芥HIT1與酵母菌Vps53p蛋白質具有若干相類似之生理功能。綜合言之，本研究率先將繫栓因子與高等植物之高溫及水份逆境耐受性連結在一起，而阿拉伯芥hit1突變株則可作為此一新研究範疇的材料。 High temperature and water stress are two major abiotic factors that often affect plant growth simultaneously in the field, implying plant responses to these stresses may be interconnected. Previously, the growth of Arabidopsis hit1-1 (heat-intolerant) mutant was found to be inhibited by both heat and water stress. In order to determine the genetic lesion underlying the hit1-1 phenotype, map-based cloning of HIT1 gene was conducted. Transformation of the hit1-1 mutant with a HIT1 cDNA clone can reverts the mutant to tolerant phenotype, confirming the identity of HIT1. Sequence analysis revealed the HIT1 gene encodes a protein of 829 amino acid residues and is homologous to yeast (Saccharomyces cerevisiae) Vps53p protein. The yeast Vps53p protein has been shown to be a tethering factor that associates with Vps52p and Vps54p in a complex formation involving in the retrograde trafficking of vesicles to the late Golgi. The growth of yeast Vps53△ null mutant also shows reduced thermotolerance, and expression of HIT1 can partially complement the defect, supporting the possibility of a conserved biological function for Vps53p and HIT1. Collectively, the hit1-1 mutant is the first mutant in higher plant linking a homolog of vesicle tethering factor to both heat and osmotic stress tolerance, providing a new field for studying plant stress responses.
