真核生物中MAPK( Mitogen-activated protein kinase)訊息傳遞路徑參與了許多發育和生理反應的過程，其中也包含了生物和非生物逆境下所誘發不同的訊息傳遞路徑。MAPK訊息傳遞路徑主要藉由MAPKKK-MAPKK-MAPK模式所引發下游的級聯反應。目前阿拉伯芥中已被確認至少有20個MAPKs、10個MAPKKs，其中前人的研究已經指出，MKK1及MKK2參與了許多生物及非生物逆境反應；然而，MKK2在金屬逆境下所扮演的角色尚未被清楚的研究。
本篇研究中，我們指出MKK2在阿拉伯芥遭遇銅逆境時扮演了很重要的調控角色，若大量表現活化MKK2會使得植物對銅逆境較具有耐受性。若將野生型、mkk2突變株、及MKK2大量活化表現的植株MKK2-EE4以銅處理七天，則會發現MKK2-EE4根部生長受抑制的情形明顯較野生型植株及mkk2突變株減緩。而相較於野生型植株及mkk2突變株，我們發現銅逆境造成的MKK2-EE4植株根部細胞死亡程度會減少，並且活性氧的產生會增加。另外，觀察細胞內的金屬離子含量，結果發現以銅處理3小時後mkk2根部細胞內銅離子的含量明顯比野生型wild type多；相較之下MKK2-EE4則比野生型wild type植株少。由結果可知在銅逆境下，MKK2的大量表現可能引發下游訊息傳遞路徑，進而影響銅離子在細胞內的含量。
綜合以上的結果，我們可推論在銅逆境下AtMKK2 可活化下游的訊息傳遞路徑並產生大量的活性氧作為訊息傳遞分子影響下游基因的表現使得銅離子在細胞內的累積較少，進而對銅逆境較有耐受性。

Eukaryotic mitogen-activated protein kinase (MAPK) signalling pathway acts downstream of receptors or sensors to transduce extracellular stimuli, including abiotic and biotic stresses, into adaptive, intracellular responses. A MAPK pathway minimally consists of a MAPKKK-MAPKK-MAPK module. The Arabidopsis thaliana MKK1 and MKK2 MAP kinase kinases have been implicated in biotic and abiotic stress responses, but the role of the MKK2 in metal signalling pathway is unknown.
In this study, we evaluated the role of the MKK2 in regulating copper stress responses in Arabidopsis . Overexpressing of MKK2 enhanced Arabidopsis resistance to copper stress. When wild type, mkk2 and MKK2-EE4 seedlings were subjected to copper treatment for 7 days, the root elongation of MKK2-EE4 plants were significantly higher than the wild type and mkk2 mutant plants. Copper induced cell death was reduced and reactive oxygen species (ROS) production was accumulated in MKK2-EE4 plants compared with wild type and mkk2 mutant plants. In addition, 200 μM copper supply resulted in higher copper concentration in mkk2 mutant roots as compared to wild type, and the copper concentration in MKK2-EE4 roots was lower than the wild type plants. Taken together these results demonstrate that MKK2 signalling is involved in Arabidopsis copper tolerance and the uptake and storage of copper are also affected by this signalling pathway.

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