分析阿拉伯芥AtGSTU7、AtGSTU8、AtGSTU18及AtGSTU25 等基因失去功能時在非生物逆境下之反應

Abstract

麩胺基硫轉移酶 (glutathione S-transferases; GST) 被熟知參與植物面對氧化逆境。然而，對於GST基因在植物體中所扮演的調控功能，目前所知仍然有限。近來我們實驗室團隊發現當GST基因tau家族中的AtGSTU17基因缺失時，植株對於鹽及乾旱的耐受性相較於野生型更為提升。有此外表型的產生主要因為AtGSTU17基因缺失時，植物體中glutathione和abscisic acid增加，對外表型產生影響。因此我們推測AtGSTU17 於植物體面對非生物性逆境時，扮演負調節者的角色。我們希望了解atgstu17所產生的外表型，是否也會出現於tau家族其他基因缺失時。我們使用atgstu7, atgstu8, atgstu18進行研究，觀察其在非生物性逆境下之功能。經由一系列非生物性逆境測試後，發現此三個基因缺失之植株於乾旱及鹽處理下，表現出和atgstu17 不同的外表型。然而在abscisic acid處理、滲透壓逆境及鹽逆境下，相對於野生型植株則有較高的發芽率。推論AtGSTU7、AtGSTU8、AtGSTU18可能於逆境之下浸潤後的種子以及幼苗發育初期，扮演負調控者的角色。此外篩選atgstu25 homozygote植株的過程中，發現取用atgstu25 hemizygote產生的子代進行分析，得到WT : hemizygote : homozygote = 1:2:0顯示當AtGSTU25缺失時，可能造成致死現象。

Glutathione S-transferases (GSTs) have been well-documented to be involved in oxidative stress metabolism. However, reports on GST gene participating in regulatory function are limited. Previously our lab had found that glutathione S-transferase U17 (AtGSTU17) knock-out plants were more tolerant to drought and salt stresses than wild-type plants. The mechanism causing these phenotypes of atgstu17 can be explained mostly by the combined effect of elevated contents of both glutathione and abscisic acid. Thus, AtGSTU17 plays a negative role in regulating abiotic stress tolerance. Three homozygous knockout mutants, atgstu7, atgstu8, atgstu18, were chosen for further study with their function in response to abiotic stress. Preliminary stress experiments indicated that the mentioned above atgstu mutants showed different phenotypes from the atgstu17 mutant plants in terms of salt and drought tolerance. However, the germination rates of the three mutants were higher than wild-type plants when they were treated with abscisic acid, salt, and osmotic stress. We suggested that these three genes might play a negative regulatory role during seed imbibitions and seedling development under stress conditions. Genetic analysis of F2 segergating population indicated that wild-type (AtGSTU25/AtGSTU25), hemizygous (AtGSTU25/atgstu25), and homozygous mutant (atgstu25/atgstu25) plants were in a ratio of 1:2:0, indicating that the homozygous mutant allele is lethal.