摘要
裂原激活蛋白激酶(MAPK)级联系统负责把接受自胞外或胞内的信号进一步传递和放大而最终作用于特异的转录因子,从而启动或调控基因的表达。MAPK信号级联系统在细胞分裂、分化、生物胁迫和非生物胁迫等多种信号传递途径中起着十分重要的作用。该文以一个茉莉酸(JA)诱导的表达序列为基础,在水稻中分离到了一个裂原激活蛋白激酶基因OsSJMK1的全长cDNA。序列比较分析表明该基因编码498个氨基酸,蛋白质等电点为8.43,包括完整的MAPK家族的蛋白激酶结构域。OsSJMK1与所有物种的MAPK一样包括蛋白激酶的全部11个次级结构域,在VII和VIII次级结构域间一个双磷酸化位点;该位点苏氨酸(T)和酪氨酸(Y)残基之间为天冬氨酸(D),而不是其他MAPK中常见的谷氨酸(E)、脯氨酸(P)或甘氨酸(G)。除了典型的MAPK激酶功能域外,在羧基端还有一段长约150个氨基酸残基的可能参与蛋白互作的结构域。以上这些结构特征表明OsSJMK1属于植物中第V类MAPK家族成员。蛋白激酶结构域序列比较表明OsSJMK1与报道的稻瘟病菌和机械伤害诱导的BWMK1的序列相似性高达81%,而且基因内含子和外显子的组成也非常相似,属于同一亚类,但在蛋白质序列的C端差异却很大。与BWMK1不同,OsSJMK1的表达不受伤害诱导,而受稻瘟病轻微诱导,但在JA和SA(水杨酸)处理早期表达量却迅速升高。在JA处理后1h,OsSJMK1转录水平升高到最大,而12h后回落到处理前的本底水平;在SA处理后30min转录水平就开始上升,2h达到最高值,而随后开始下降到处理前的本底水平。SA类似物BTH也能诱导OsSJMK1的表达。其他一些激素处理(如ABA)和非生物胁迫(如干旱、盐胁迫)都不对基因的表达产生任何影响,而且在植物大部分组织中的表达量都非常低。这些结果说明OsSJMK1可能特异性的参与JA和SA介导的防卫反应。
On the basis of a JA-inducible EST, the full length cDNA of a putative protein kinase gene, OsSJMK1, was isolated from rice （Oryza sativa L.）. The predicted protein of this gene, consisting of 498 amino acids with a predicted PI value of 8.43, contains a mitogen-activated protein kinase （MAPK） domain with a dual-phosphorylation activation motif TDY （Thr-Asp-Tyr） and a C-terminus domain that feature a typical MAPK belonging to subgroup V. OsSJMK1 showed 81% sequence identity to the reported BWMK1, a blast fungus and wounding inducible protein, in the N-terminus kinase domain but had low sequence identity in the C-terminus domain. Despite the high similarity of gene structure between OsSJMK1 and BWMK1, the expression of OsSJMK1 was weakly induced by blast fungus but not wounding, rather it was transiently induced by jasmonic acid （JA） and salicylic acid （SA） at early stages of treatment. This gene was not induced by other hormones （such as ABA） or abiotic stresses, such as drought and salinity. The low level of transcript of this gene was detected in the various tissues of rice. The results suggest that OsSJMK1 might be activated specifically by JA and SA and involved in defense signaling pathways.
基金
This work was supported by the National Natural Science Foundation of China (No. 30370735) and the National High-Tech Re-search and Development (No. 2002AA2Z1002).
