Salicylic acid stimulates secretion of the normally symplastic enzyme mannitol dehydrogenase: a possible defense against mannitol-secreting fungal pathogens
Salicylic acid stimulates secretion of the normally symplastic enzyme mannitol dehydrogenase: a possible defense against mannitol-secreting fungal pathogens
复制标题
DOI：
10.1007/s00425-009-1006-3
复制
发表时间：
2009-11-01
期刊：
影响因子：
4.3
通讯作者：
Williamson, John D.
中科院分区：
文献类型：
--
作者：
Cheng, Fang-yi;Zamski, Eli;Williamson, John D.
糖醇甘露醇是一种重要的碳水化合物，在许多植物和真菌的代谢和渗透保护中都起着重要的作用。除了这些传统上公认的作用外，甘露醇据报道是一种抗氧化剂，因此可能在宿主-病原体相互作用中发挥作用。目前的研究表明，病原真菌可以分泌甘露醇到外质体中，以抑制活性氧介导的宿主防御。本文报道的免疫电镜、免疫印迹和生化数据显示，在内源性植物防御反应诱导剂水杨酸（SA）处理后，正常的共塑植物酶甘露醇脱氢酶（MTD）分泌到外质体中。相反，一种细胞质标记蛋白，己糖激酶，在sa处理后仍保留在细胞质中。分泌的MTD在输出到外质体后仍保持活性。鉴于MTD将甘露醇转化为甘露糖，MTD的分泌可能是植物防御甘露醇分泌真菌病原体（如Alternaria）的重要组成部分。经SA处理后，高尔基体中未检测到MTD，其SA诱导的分泌对高尔基蛋白介导的蛋白质运输抑制剂brefeldin A具有抗性。再加上MTD蛋白上缺乏已知的细胞外靶向序列，这些数据表明，植物对病原体攻击的反应可能包括通过尚未表征的非高尔基机制分泌选择性防御蛋白。
The sugar alcohol mannitol is an important carbohydrate with well-documented roles in both metabolism and osmoprotection in many plants and fungi. In addition to these traditionally recognized roles, mannitol is reported to be an antioxidant and as such may play a role in host-pathogen interactions. Current research suggests that pathogenic fungi can secrete mannitol into the apoplast to suppress reactive oxygen-mediated host defenses. Immunoelectron microscopy, immunoblot, and biochemical data reported here show that the normally symplastic plant enzyme, mannitol dehydrogenase (MTD), is secreted into the apoplast after treatment with the endogenous inducer of plant defense responses salicylic acid (SA). In contrast, a cytoplasmic marker protein, hexokinase, remained cytoplasmic after SA-treatment. Secreted MTD retained activity after export to the apoplast. Given that MTD converts mannitol to the sugar mannose, MTD secretion may be an important component of plant defense against mannitol-secreting fungal pathogens such as Alternaria. After SA treatment, MTD was not detected in the Golgi apparatus, and its SA-induced secretion was resistant to brefeldin A, an inhibitor of Golgi-mediated protein transport. Together with the absence of a known extracellular targeting sequence on the MTD protein, these data suggest that a plant's response to pathogen challenge may include secretion of selected defensive proteins by as yet uncharacterized, non-Golgi mechanisms.