Plant Physiology：中科院遗传发育所揭示水稻乙烯信号转导及调控盐

摘要 : 植物气体激素乙烯在植物生长发育以及应对逆境胁迫过程中起着重要作用。在拟南芥中，已经建立了一个从乙烯信号接收到转录调控的线性乙烯信号转导模型。然而，在单子叶植物，尤其是水稻中的乙烯信号转导的作用机制还不甚清楚。

植物气体激素乙烯在植物生长发育以及应对逆境胁迫过程中起着重要作用。在拟南芥中，已经建立了一个从乙烯信号接收到转录调控的线性乙烯信号转导模型。然而，在单子叶植物，尤其是水稻中的乙烯信号转导的作用机制还不甚清楚。

中国科学院遗传与发育生物学研究所张劲松研究组和陈受宜研究组分离鉴定了一系列的水稻乙烯反应突变体并对其中的mhz6进行了深入研究。通过图位克隆发现MHZ6编码了一个和南芥EIN3同源的转录因子OsEIL1。MHZ6/OsEIL1 的突变会导致水稻黄化苗的根对乙烯完全不敏感，而干扰其家族基因OsEIL2 的表达则导致了胚芽鞘对乙烯的不敏感，这表明MHZ6/OsEIL1 和OsEIL2 分别调控了水稻黄化苗根和胚芽鞘的乙烯反应。进一步的研究还发现MHZ6/OsEIL1 和OsEIL2 通过直接结合并激活OsHKT2;1 的在水稻幼苗根中表达，从而促进了植物对钠离子的吸收，导致植株对盐敏感。而突变体和RNAi幼苗表现出抗盐的表型。进一步用乙烯或1-MCP(乙烯信号转导抑制剂)处理对照水稻，则分别造成盐敏感和耐盐的表型。这些研究揭示了水稻乙烯信号转导及调控盐胁迫反应的新机制。在拟南芥中，乙烯信号转导途径的转录因子EIN3和EIL1在调控乙烯反应上没有器官特异性，且乙烯信号转导促进耐盐性。而在水稻中，MHZ6/OsEIL1和OsEIL2分别调控根和胚芽鞘的乙烯反应。二者可通过促进根对钠离子吸收达到水环境下的离子平衡使植株正常生长，但高盐下导致水稻盐敏感(如图)。

该研究结果于5月20日在线发表于Plant Physiology(DOI:10.1104/pp.15.00353)。博士生杨超和工作人员马彪是该论文的共同第一作者。该项研究得到国家自然科学基金和“973”计划等项目的资助。


图：水稻和拟南芥的乙烯信号转导途径对于幼苗乙烯反应和盐胁迫反应的调控机制比较。水稻中MHZ6/OsEIL1和OsEIL2分别调控根和胚芽鞘的乙烯反应，也可激活钠离子转运蛋白基因OsHKT2;1表达，促进根对钠离子吸收保持水环境下细胞的离子平衡，使植株正常生长。但高盐下因过量吸收钠离子可导致盐敏感。在拟南芥中，EIN3和EIL1对乙烯反应的调控没有器官特异性，但可提高植物耐盐性。

原文链接：

MHZ6/OsEIL1 and OsEIL2 Regulate Ethylene Response of Roots and Coleoptiles and Negatively Affect Salt Tolerance in Rice.

原文摘要：

Ethylene plays important roles in plant growth and development and stress responses. The ethylene signaling pathway has been extensively studied mainly in Arabidopsis. However，the molecular mechanism of ethylene signaling is largely unknown in rice. Previously, we have isolated a set of rice ethylene-response mutants. Here, we characterized the mutant mhz6. Through map-based cloning, we found that MHZ6 encodes OsEIL1, a rice homolog of EIN3, which is the master transcriptional regulator of ethylene signaling in Arabidopsis. Disruption of MHZ6/OsEIL1 caused ethylene insensitivity mainly in roots, whereas silencing of the closely-related OsEIL2 led to ethylene insensitivity mainly in coleoptiles of etiolated seedlings. This organ-specific functional divergence is different from the functional features of EIN3 and EIL1, both of which mediate the incomplete ethylene-responses of Arabidopsis etiolated seedlings. In Arabidopsis, EIN3 and EIL1 play positive roles in plant salt tolerance. In rice, however, lack of MHZ6/OsEIL1 or OsEIL2 functions improves salt tolerance, whereas the overexpression lines exhibits salt hypersensitivity at seedling stage, indicating that MHZ6/OsEIL1 and OsEIL2 negatively regulate salt tolerance in rice. Furthermore, this negative regulation by MHZ6/OsEIL1 and OsEIL2 in salt tolerance is likely in part attributable to the direct regulation of OsHKT2;1 expression and Na+ uptake in roots. Additionally, MHZ6/OsEIL1 overexpression promotes grain size and thousand-grain-weight. Together, our study provides insights for functional diversification of MHZ6/OsEIL1 and OsEIL2 in ethylene response and finds a novel mode of ethylene-regulated salt stress response which could be helpful for engineering salt-tolerant crops.

作者：张劲松&陈受宜

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