阿拉伯芥AtGSTU17與PHYA在光、荷爾蒙及逆境的功能研究

Abstract

植物多為固著生長，行光合作用，因此因應外界光線環境的改變，而調整自身的生長與發育能力，對植物尤其重要。在阿拉伯芥中，光敏素A 是負責接收遠紅光，並透過一連串的訊息傳遞而影響下游的基因表現，使植物進行光型態發生（photomorphogenesis）。前人研究指出GST 基因家族成員AtGSTU17在遠紅光中的基因表現量可受到phyA及其下游基因FIN219突變所抑制，隨著遠紅光強度越強，AtGSTU17也表現越多。在較弱的遠紅光下Atgstu17突變體呈現較野生型長的下胚 軸，顯示AtGSTU17的表現與遠紅光光照有密切的關係。但AtGSTU17在遠紅光中作用的分子機制尚未明瞭。利用遠紅光及PCR 篩選到Atgstu17phyA的雙突變體，從外表型的檢測，發現Atgstu17phyA的下胚軸長度在弱遠紅光下比親代各別的單突變體長。暗示AtGSTU17與phyA在遠紅光下有非等位非互補（nonallelic noncomplementation）的遺傳調控關係，可能分別調控同一訊息傳遞下的兩個平行途徑，或者兩者有相互作用的功能。另外，當AtGSTU17大量表現在phyA突變體(AtGSTU17OE-2/phyA)，在遠紅光下的下胚軸長度比phyA突變體還短。然而，RT-PCR指出Atgstu17突變體在遠紅光下有幾個與auxin相關的基因表現增加，而PIFs及光訊息相關的基因(例如: CHS)的表現則是下降的。此外，在Atgstu17突變體有幾個受ABA調控的基因表現也受到影響。在鹽類逆境及滲透壓逆境處理之下，我們發現gstu17突變體對於逆境造成的側根抑制不敏感，這顯示 AtGSTU17可能有參與在逆境方面的調控。綜合上述結果顯示AtGSTU17的表現會受到遠紅光、荷爾蒙、逆境的調控，並且會影響植物在遠紅光下的光型態發生及荷爾蒙、逆境所控制的根部發育。

Phytochrome A (phyA) is the photoreceptor of far-red (FR) light. Previous studies have shown that a glutathione S-transferase (AtGSTU17), a tau class member of the GST gene family in Arabidopsis, can be induced rapidly in wild type under FR light, but abolished in the phyA mutant. The molecular mechanisms underlying the regulation of GSTU17 expression by phyA remain unknown. We isolated the gstu17phyA double mutant showing that it exhibited a longer hypocotyl phenotype than its parental lines specifically under weak FR light. When AtGSTU17 was overexpressed in the phyA mutant background (GSTU17OE-2/phyA), it led to a shorter hypocotyl phenotype than the phyA under FR light. These data suggest that AtGSTU17 and PHYA act as a nonallelic noncomplementary relation, and may work in parallel pathways or physically interact with each other to control hypocotyl elongation under FR. Furthermore, RT-PCR analyses indicated that several auxin responsive genes were up-regulated, and phytochrome-interacting factors (PIFs) as well as light responsive gene such as CHS down-regulated in the gstu17 mutant under FR. In addition, several ABA-regualted genes were affected in the gstu17 mutant. Under the ionic stress and osmotic stress treatments, the gstu17 mutant is hyposensitive in terms of lateral roots inhibition. Taken together, these data indicate that AtGSTU17 may function as a crosstalk among phyA-mediated FR light, auxin, ABA and stress signaling pathways to regulate hypocotyl elongation and root development in Arabidopsis.