Covic L, Silva N F, Lew R R
Department of Biology, York University, 4700 Keele Street, Toronto, Ont., Canada.
Biochim Biophys Acta. 1999 Sep 21;1451(2-3):242-54. doi: 10.1016/s0167-4889(99)00096-8.
The Arabidopsis thaliana ARAKIN (ATMEKK1) gene shows strong homology to members of the (MAP) mitogen-activated protein kinase family, and was previously shown to functionally complement a mating defect in Saccharomyces cerevisiae at the level of the MEKK kinase ste11. The yeast STE11 is an integral component of two MAP kinase cascades: the mating pheromone pathway and the HOG (high osmolarity glycerol response) pathway. The HOG signal transduction pathway is activated by osmotic stress and causes increased glycerol synthesis. Here, we first demonstrate that ATMEKK1 encodes a protein with kinase activity, examine its properties in yeast MAP kinase cascades, then examine its expression under stress in A. thaliana. Yeast cells expressing the A. thaliana ATMEKK1 survive and grow under high salt (NaCl) stress, conditions that kill wild-type cells. Enhanced glycerol production, observed in non-stressed cells expressing ATMEKK1 is the probable cause of yeast survival. Downstream components of the HOG response pathway, HOG1 and PBS2, are required for ATMEKK1-mediated yeast survival. Because ATMEKK1 functionally complements the sho1/ssk2/ssk22 triple mutant, it appears to function at the level of the MEKK kinase step of the HOG response pathway. In A. thaliana, ATMEKK1 expression is rapidly (within 5 min) induced by osmotic (NaCl) stress. This is the same time frame for osmoticum-induced effects on the electrical properties of A. thaliana cells, both an immediate response and adaptation. Therefore, we propose that the A. thaliana ATMEKK1 may be a part of the signal transduction pathway involved in osmotic stress.
拟南芥ARAKIN（ATMEKK1）基因与（MAP）丝裂原活化蛋白激酶家族成员具有高度同源性，先前已证明其在MEKK激酶ste11水平上可功能性互补酿酒酵母中的交配缺陷。酵母STE11是两个MAP激酶级联反应的重要组成部分：交配信息素途径和HOG（高渗甘油应答）途径。HOG信号转导途径由渗透胁迫激活，并导致甘油合成增加。在此，我们首先证明ATMEKK1编码一种具有激酶活性的蛋白质，研究其在酵母MAP激酶级联反应中的特性，然后研究其在拟南芥胁迫条件下的表达。表达拟南芥ATMEKK1的酵母细胞在高盐（NaCl）胁迫下能够存活并生长，而这种条件会杀死野生型细胞。在表达ATMEKK1的非胁迫细胞中观察到的甘油产量增加可能是酵母存活的原因。HOG应答途径的下游组分HOG1和PBS2是ATMEKK1介导的酵母存活所必需的。由于ATMEKK1在功能上互补sho1/ssk2/ssk22三重突变体，它似乎在HOG应答途径的MEKK激酶步骤发挥作用。在拟南芥中，ATMEKK1的表达在渗透（NaCl）胁迫下迅速（在5分钟内）被诱导。这与渗透剂对拟南芥细胞电特性的影响在同一时间范围内，包括即时反应和适应性反应。因此，我们提出拟南芥ATMEKK1可能是参与渗透胁迫信号转导途径的一部分。
