AtMAPR3 的功能可能與高溫逆境有關且其表現之調控 與ascorbate-glutathione cycle 有關

Abstract

活性氧化物 (ROS) 為生物體內氧代謝的副產物，除了會造成細胞中分子的損壞，也會參與細胞內的訊息傳導抵禦氧化逆境。阿拉伯芥蛋白 Membrane-Associated Progesterone Receptor 3 in Arabidopsis thaliana (AtMAPR3)基因的表現量會被H2O2和tert-butyl hydroxide (tBHP) 等會產生氧化逆境的處理所誘導，也會被抗氧化劑ascorbate誘導。此外，ATMAPR3也被發現會和參與光呼吸作用的alanine-glyoxylate aminotransferase 1 (AGT1) 進行交互作用。這些發現顯示ROS可能會藉由調控AtMAPR3的基因表現量幫助阿拉伯芥適應氧化逆境。 本研究中進一步發現AtMAPR3的基因表現會被ascorbate-glutathione cycle中的組成分子所誘導，其中以ascorbate最明顯；有趣的是，ascorbate造成的誘導在ascorbate peroxidase 1 (apx1) 和ascorbate peroxidase 2 (apx2) 突變株中會減弱, 但在thylakoid ascorbate peroxidase (tapx) 突變株中並沒有此現象。另外，利用「粒線體螢光標定突變株」 mt-ck進行螢光定位，發現部分AtMAPR3會與粒線體共定位 (colocalization)。在高溫的環境下 (35ºC)，AtMAPR3基因剔除突變株 (AtMAPR3-KO) 的存活率 (33%) 低於野生種 (59%)，而AtMAPR3基因過量表現突變株 (AtMAPR3-OX) 的存活率 (71%) 則略高於野生種。本研究中發現，AtMAPR3 可能會被ROS由不同訊息傳導路徑調控，且AtMAPR3可能幫助阿拉伯芥適應熱逆境。

Reactive oxygen species (ROS), though generated as toxic byproducts in aerobic metabolism, are involved in defense against oxidative stresses by participating in cellular signaling. The gene expression of Membrane-Associated Progesterone Receptor 3 in Arabidopsis thaliana (AtMAPR3) has been found to be induced by externally supplied H2O2 and tBHP (tert-butyl hydroxide), which are both considered to generate ROS stresses. It is also induced by ascorbate, an ROS scavenger. AtMAPR3 interacts with alanine-glyoxylate aminotransferase 1 (AGT1), a component in photorespiration. These findings suggests that the regulation of AtMAPR3 by ROS may enable Arabidopsis to adapt to ROS-generating conditions. In this study, the regulation of AtMAPR3 expression was further investigated. AtMAPR3 expression was induced by several components in the ascorbate-glutathione cycle, especially ascorbate; interestingly, the induction by ascorbate was reduced in ascorbate peroxidase 1 (apx1) and ascorbate peroxidase 2 (apx2) mutants, but not in a thylakoid ascorbate peroxidase (tapx) mutant. AtMAPR3 partially colocalized with mitochondria as revealed by fluorescence microscopy using the mt-ck mutant, which expresses mitochondria-targeted CFP. Under high temperature conditions (35ºC), the survival rate of the AtMAPR3 knockout mutant (33%) was lower compared to wild type (59%), while that of the AtMAPR3 overexpression mutant (71%) was slightly higher. In summary, AtMAPR3 may be regulated by ROS signaling via different pathways and AtMAPR3 might function in helping Arabidopsis cope with high temperature stress.