Chen Junping, Burke John J, Xin Zhanguo, Xu Changcheng, Velten Jeff
Plant Stress and Germplasm Development Unit, USDA-ARS, 3810 4th Street, Lubbock, TX 79415, USA.
Plant Cell Environ. 2006 Jul;29(7):1437-48. doi: 10.1111/j.1365-3040.2006.01527.x.
Plants are constantly challenged with various abiotic stresses in their natural environment. Elevated temperatures have a detrimental impact on overall plant growth and productivity. Many plants increase their tolerance to high temperatures through an adaptation response known as acquired thermotolerance. To identify the various mechanisms that plants have evolved to cope with high temperature stress, we have isolated a series of Arabidopsis mutants that are defective in the acquisition of thermotolerance after an exposure to 38 degrees C, a treatment that induces acquired thermotolerance in wild-type plants. One of these mutants, atts02, was not only defective in acquiring thermotolerance after the treatment, but also displayed a reduced level of basal thermotolerance in a 30 degrees C growth assay. The affected gene in atts02 was identified by positional cloning and encodes digalactosyldiacylglycerol synthase 1 (DGD1) (the atts02 mutant was, at that point, renamed dgd1-2). An additional dgd1 allele, dgd1-3, was identified in two other mutant lines displaying altered acquired thermotolerance, atts100 and atts104. Expression patterns of several heat shock proteins (HSPs) in heat-treated dgd1-2 homozygous plants were similar to those from identically treated wild-type plants, suggesting that the thermosensitivity in the dgd1-2 mutant was not caused by a defect in HSP induction. Lipid analysis of wild-type and mutant plants indicated a close correlation between the ability to acquire thermotolerance and the increases in digalactosyldiacylglycerol (DGDG) level and in the ratio of DGDG to monogalactosyldiacylglycerol (MGDG). Thermosensitivity in dgd1-2 and dgd1-3 was associated with (1) a decreased DGDG level and (2) an inability to increase the ratio of DGDG to MGDG upon exposure to a 38 degrees C sublethal temperature treatment. Our results suggest that the DGDG level and/or the ratio of DGDG to MGDG may play an important role in basal as well as acquired thermotolerance in Arabidopsis.
在自然环境中，植物不断面临各种非生物胁迫。温度升高会对植物的整体生长和生产力产生不利影响。许多植物通过一种称为获得性耐热性的适应反应来提高对高温的耐受性。为了确定植物进化出的应对高温胁迫的各种机制，我们分离了一系列拟南芥突变体，这些突变体在暴露于38摄氏度（该处理可诱导野生型植物产生获得性耐热性）后，获得耐热性的能力存在缺陷。其中一个突变体atts02，不仅在处理后获得耐热性方面存在缺陷，而且在30摄氏度生长试验中基础耐热性水平也降低。通过定位克隆确定了atts02中受影响的基因，其编码二半乳糖基二酰基甘油合酶1（DGD1）（此时atts02突变体重新命名为dgd1-2）。在另外两个显示获得性耐热性改变的突变体品系atts100和atts104中，鉴定出了另一个dgd1等位基因dgd1-3。热处理的dgd1-2纯合植物中几种热休克蛋白（HSP）的表达模式与相同处理的野生型植物相似，这表明dgd1-2突变体中的热敏感性不是由HSP诱导缺陷引起的。对野生型和突变体植物的脂质分析表明，获得耐热性的能力与二半乳糖基二酰基甘油（DGDG）水平的增加以及DGDG与单半乳糖基二酰基甘油（MGDG）的比率增加密切相关。dgd1-2和dgd1-3中的热敏感性与（1）DGDG水平降低和（2）暴露于38摄氏度亚致死温度处理时无法增加DGDG与MGDG的比率有关。我们的结果表明，DGDG水平和/或DGDG与MGDG的比率可能在拟南芥的基础耐热性和获得性耐热性中起重要作用。
