植物因無法自由的移動，所以時刻都有可能面臨不適合生存的環境逆境。高溫逆境為主要的環境逆境之一。高溫會影響植物的生長及其產量。植物為了抵抗高溫逆境，必需演化出適當的保護機制。為了瞭解植物所演化出抵禦高溫逆境的機制，以及調控這些機制的遺傳因子，我們以前向式遺傳研究法(forward genetics approach)，利用化學突變劑甲基磺酸乙酯(ethylmethane sulfonate, EMS)篩選出兩株突變植株。其一為對長時間高溫敏感之突變株，命名為heat sensitive 49 (hs49)。其二為可耐受短時間熱休克逆境之突變株，命名為78hs (78 heat shock)。實驗結果顯示，hs49突變位址，是在阿拉伯芥AGI map 第五條染色體上，25,860 kb - 25,966 kb的區間範圍內。78hs突變位址，則是在阿拉伯芥編號At5g40280基因的第二個intron上，第134個鹼基由A變成T的突變點。此突變點經序列分析後，發現其為RNA splice辨認之處。過去有關At5g40280的研究指出，此基因突變或表現量降低時，會使植物對ABA具有過度敏感的性狀，且比野生種植株更能耐受乾旱逆境。生理實驗發現的結果也顯示出，78hs確實對ABA過度敏感，對乾旱逆境也有更高的耐受能力。然而，At5g40280如何保護植物免於高溫傷害之機制，仍然未知。;Plants, being immobile and can not escape from their growing environments, are vulnerable to various environmental stresses and must develop effective protecting mechanisms for survival. One of the most typical environmental stresses plants encounter is high temperature stress. Heat temperature can affect plant growth and development. In aggriulature, high temperature can affect crop yield. In order to identify the genetic determinant that are essential for plant to cope with high temperature stress, hence better improve heat tolerance in crop, we have used a forward genetics approach to screen for mutants of Arabidopsis that have altered responses to high temperatures. Two mutants were isolated after ethyl-methane sulfonate (EMS)-mutagenesis. While hs49 (heat sensitive 49) is isolated because of its inability to tolerate sustained high temperature stress, 78hs (78 heat shock) is isolated because of its ability to tolerate heat shock stress. To identify the mutated loci of hs49 and 78hs, map-based cloning procedures was conducted. Results indicated that hs49 is located at a region between AGI map 25,860 kb-25,966 kb of the chromosome Ⅴ. The 78hs locus is mapped to At5g40280 gene. The mutation of 78hs is a single nucleotide change from A to T at the RNA splicing recongnized site of the 2nd intron. Previous studies have shown that At5g40280 null or down-regulrated plants are hypersensitive to ABA and can tolerate drought stress compare to those of wild-type. Physiological experiments showed that 78hs exhibits those previously described phenotypes. Nevertheless, the mechanisms by which 78HS contributes to protect plants against high temperature injuries are still unknown.
