Ishitani M, Xiong L, Lee H, Stevenson B, Zhu J K
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Plant Cell. 1998 Jul;10(7):1151-61. doi: 10.1105/tpc.10.7.1151.
Low-temperature stress induces the expression of a variety of genes in plants. However, the signal transduction pathway(s) that activates gene expression under cold stress is poorly understood. Mutants defective in cold signaling should facilitate molecular analysis of plant responses to low temperature and eventually lead to the identification and cloning of a cold stress receptor(s) and intracellular signaling components. In this study, we characterize a plant mutant affected in its response to low temperatures. The Arabidopsis hos1-1 mutation identified by luciferase imaging causes superinduction of cold-responsive genes, such as RD29A, COR47, COR15A, KIN1, and ADH. Although these genes are also induced by abscisic acid, high salt, or polyethylene glycol in addition to cold, the hos1-1 mutation only enhances their expression under cold stress. Genetic analysis revealed that hos1-1 is a single recessive mutation in a nuclear gene. Our studies using the firefly luciferase reporter gene under the control of the cold-responsive RD29A promoter have indicated that cold-responsive genes can be induced by temperatures as high as 19 degrees C in hos1-1 plants. In contrast, wild-type plants do not express the luciferase reporter at 10 degrees C or higher. Compared with the wild type, hos1-1 plants are l ess cold hardy. Nonetheless, after 2 days of cold acclimation, hos1-1 plants acquired the same degree of freezing tolerance as did the wild type. The hos1-1 plants flowered earlier than did the wild-type plants and appeared constitutively vernalized. Taken together, our findings show that the HOS1 locus is an important negative regulator of cold signal transduction in plant cells and that it plays critical roles in controlling gene expression under cold stress, freezing tolerance, and flowering time.
低温胁迫会诱导植物中多种基因的表达。然而，在冷胁迫下激活基因表达的信号转导途径尚不清楚。冷信号缺陷的突变体应有助于对植物对低温反应的分子分析，并最终导致鉴定和克隆冷胁迫受体及细胞内信号成分。在本研究中，我们对一个在低温反应中受到影响的植物突变体进行了表征。通过荧光素酶成像鉴定的拟南芥hos1-1突变导致冷响应基因如RD29A、COR47、COR15A、KIN1和ADH的超诱导。尽管这些基因除了冷胁迫外还可被脱落酸、高盐或聚乙二醇诱导，但hos1-1突变仅在冷胁迫下增强它们的表达。遗传分析表明，hos1-1是一个核基因中的单隐性突变。我们使用在冷响应性RD29A启动子控制下的萤火虫荧光素酶报告基因进行的研究表明，在hos1-1植物中，高达19摄氏度的温度可诱导冷响应基因。相比之下，野生型植物在10摄氏度或更高温度下不表达荧光素酶报告基因。与野生型相比，hos1-1植物的抗寒能力较弱。然而，经过2天的冷驯化后，hos1-1植物获得了与野生型相同程度的耐冻性。hos1-1植物比野生型植物开花早，并且表现出组成型春化。综上所述，我们的研究结果表明，HOS1基因座是植物细胞冷信号转导的重要负调控因子，并且在冷胁迫下控制基因表达、耐冻性和开花时间方面发挥关键作用。
