Wang Jie, Pan Changtian, Wang Yan, Ye Lei, Wu Jian, Chen Lifei, Zou Tao, Lu Gang
Department of Horticulture, Zhejiang University, Hangzhou, 310058, China.
Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Ministry of Agriculture, Hangzhou, 310058, China.
BMC Genomics. 2015 May 15;16(1):386. doi: 10.1186/s12864-015-1621-2.
The mitogen-activated protein kinase (MAPK) cascade consists of three types of reversibly phosphorylated kinases, namely, MAPK, MAPK kinase (MAPKK/MEK), and MAPK kinase kinase (MAPKKK/MEKK), playing important roles in plant growth, development, and defense response. The MAPK cascade genes have been investigated in detail in model plants, including Arabidopsis, rice, and tomato, but poorly characterized in cucumber (Cucumis sativus L.), a major popular vegetable in Cucurbitaceae crops, which is highly susceptible to environmental stress and pathogen attack.
A genome-wide analysis revealed the presence of at least 14 MAPKs, 6 MAPKKs, and 59 MAPKKKs in the cucumber genome. Phylogenetic analyses classified all the CsMAPK and CsMAPKK genes into four groups, whereas the CsMAPKKK genes were grouped into the MEKK, RAF, and ZIK subfamilies. The expansion of these three gene families was mainly contributed by segmental duplication events. Furthermore, the ratios of non-synonymous substitution rates (Ka) and synonymous substitution rates (Ks) implied that the duplicated gene pairs had experienced strong purifying selection. Real-time PCR analysis demonstrated that some MAPK, MAPKK and MAPKKK genes are preferentially expressed in specific organs or tissues. Moreover, the expression levels of most of these genes significantly changed under heat, cold, drought, and Pseudoperonospora cubensis treatments. Exposure to abscisic acid and jasmonic acid markedly affected the expression levels of these genes, thereby implying that they may play important roles in the plant hormone network.
A comprehensive genome-wide analysis of gene structure, chromosomal distribution, and evolutionary relationship of MAPK cascade genes in cucumber are present here. Further expression analysis revealed that these genes were involved in important signaling pathways for biotic and abiotic stress responses in cucumber, as well as the response to plant hormones. Our first systematic description of the MAPK, MAPKK, and MAPKKK families in cucumber will help to elucidate their biological roles in plant.
丝裂原活化蛋白激酶（MAPK）级联由三种可逆磷酸化的激酶组成，即MAPK、MAPK激酶（MAPKK/MEK）和MAPK激酶激酶（MAPKKK/MEKK），在植物生长、发育和防御反应中发挥重要作用。MAPK级联基因已在拟南芥、水稻和番茄等模式植物中得到详细研究，但在葫芦科作物中一种主要的常见蔬菜黄瓜（Cucumis sativus L.）中其特征了解较少，黄瓜对环境胁迫和病原体攻击高度敏感。
全基因组分析表明黄瓜基因组中至少存在14个MAPK、6个MAPKK和59个MAPKKK。系统发育分析将所有CsMAPK和CsMAPKK基因分为四组，而CsMAPKKK基因则分为MEKK、RAF和ZIK亚家族。这三个基因家族的扩张主要由片段重复事件导致。此外，非同义替换率（Ka）和同义替换率（Ks）的比值表明重复的基因对经历了强烈的纯化选择。实时PCR分析表明，一些MAPK、MAPKK和MAPKKK基因在特定器官或组织中优先表达。此外，这些基因中的大多数在热、冷、干旱和黄瓜霜霉病菌处理下表达水平显著变化。暴露于脱落酸和茉莉酸显著影响这些基因的表达水平，从而表明它们可能在植物激素网络中发挥重要作用。
本文对黄瓜中MAPK级联基因的基因结构、染色体分布和进化关系进行了全面的全基因组分析。进一步的表达分析表明，这些基因参与了黄瓜中生物和非生物胁迫反应以及对植物激素反应的重要信号通路。我们对黄瓜中MAPK、MAPKK和MAPKKK家族的首次系统描述将有助于阐明它们在植物中的生物学作用。
