Department of Horticultural Science, North Carolina State University, Raleigh, NC, USA.
Plant Signal Behav. 2010 Feb;5(2):129-31. doi: 10.4161/psb.5.2.10304. Epub 2010 Feb 11.
The sugar alcohol mannitol and it’s catabolic enzyme mannitol dehydrogenase (MTD), in addition to welldocumented roles in metabolism and osmoprotection, may play roles in hostpathogen interactions. Research suggests that in response to the mannitol that pathogenic fungi secrete to suppress reactive oxygen-mediated host defenses, plants make MTD to catabolize fungal mannitol. Yet previous work suggested that pathogen-secreted mannitol is extracellular, while in healthy plants MTD is cytoplasmic. We have presented results showing that the normally cytoplasmic MTD is exported into the cell wall or extracellular space in response to the endogenous inducer of plant defense responses salicylic acid (SA). This SA-induced secretion is insensitive to brefeldin A, an inhibitor of Golgimediated protein transport. Together with the absence of MTD in Golgi stacks and the lack of a documented extracellular targeting sequence in the MTD protein, this suggests MTD is secreted by a non-Golgi, pathogen-activated secretion mechanism in plants. Here we discuss the potential significance of non-Golgi secretion in response to stress.
糖醇甘露醇及其分解代谢酶甘露醇脱氢酶（MTD）除了在代谢和渗透保护中具有明确的作用外，还可能在宿主-病原体相互作用中发挥作用。研究表明，植物为了分解真菌甘露醇，会在受到致病真菌分泌的甘露醇抑制活性氧介导的宿主防御后产生 MTD。然而，之前的工作表明，病原体分泌的甘露醇是细胞外的，而在健康植物中，MTD 是细胞质的。我们提出的结果表明，正常存在于细胞质中的 MTD 会响应植物防御反应的内源性诱导物水杨酸（SA）被输出到细胞壁或细胞外空间。这种由 SA 诱导的分泌对布雷菲德菌素 A（一种抑制高尔基体介导的蛋白质运输的抑制剂）不敏感。再加上 MTD 不存在于高尔基体堆栈中，并且在 MTD 蛋白中没有记录到细胞外靶向序列，这表明 MTD 是通过植物中一种非高尔基体、病原体激活的分泌机制分泌的。在这里，我们讨论了应激反应中非高尔基体分泌的潜在意义。
