Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, USA.
Fungal Genet Biol. 2012 Oct;49(10):802-13. doi: 10.1016/j.fgb.2012.07.006. Epub 2012 Aug 10.
"Two-component" histidine kinase (HSK1) is the primary regulator of resistance to sugar osmotic stress and sensitivity to dicarboximide or phenylpyrrole fungicides in the citrus fungal pathogen Alternaria alternata. On the other hand, the mitogen-activated protein kinase HOG1 confers resistance solely to salts and oxidative stress. We report here independent and shared functions of the SKN7-mediated signaling pathway with HSK1 and HOG1. SKN7, a putative transcription downstream regulator of HSK1, is primarily required for cellular resistance to oxidative and sugar-induced osmotic stress. SKN7, perhaps acting in parallel with HOG1, is required for resistance to H(2)O(2), tert-butyl hydroperoxide, and cumyl peroxide, but not to the superoxide-generating compounds - menadione, potassium superoxide, and diamide. Because of phenotypic commonalities, SKN7 is likely involved in resistance to sugar-induced osmotic stress via the HSK1 signaling pathway. However, mutants lacking SKN7 displayed wild-type sensitivity to NaCl and KCl salts. SKN7 is constitutively localized in the nucleus regardless of H(2)O(2) treatment. When compared to the wild type, skn7 mutants exhibited lower catalase, peroxidase, and superoxide dismutase activities and induced significantly fewer necrotic lesions on the susceptible citrus cultivar. The skn7 mutant exhibited fungicide resistance at levels between the hsk1 and the hog1 mutant strains. Skn7/hog1 double mutants exhibited fungicide resistance, similar to the strain with a single AaHSK1 gene mutation. Moreover, the A. alternata SKN7 plays a role in conidia formation. Conidia produced by the skn7 mutant are smaller and have fewer transverse septae than those produced by wild type. All altered phenotypes in the mutant were restored by introducing and expressing a wild-type copy of SKN7 under control of the endogenous promoter.
"双组分"组氨酸激酶（HSK1）是柑橘真菌病原体Alternaria alternata 抵抗糖渗透胁迫和对二羧基酰亚胺或苯并吡咯类杀菌剂敏感的主要调节剂。另一方面，丝裂原激活蛋白激酶 HOG1 仅赋予对盐和氧化应激的抗性。我们在这里报告 SKN7 介导的信号通路与 HSK1 和 HOG1 的独立和共享功能。SKN7，作为 HSK1 的下游转录调节因子的假定转录因子，主要需要细胞抵抗氧化和糖诱导的渗透胁迫。SKN7，也许与 HOG1 平行作用，需要抵抗 H2O2、叔丁基过氧化物和过氧化枯烯，但不需要超氧化物生成化合物 - 甲萘醌、超钾和二酰胺。由于表型的相似性，SKN7 可能通过 HSK1 信号通路参与抵抗糖诱导的渗透胁迫。然而，缺乏 SKN7 的突变体对 NaCl 和 KCl 盐显示出野生型敏感性。SKN7 无论 H2O2 处理与否，都在核内固有定位。与野生型相比，skn7 突变体表现出较低的过氧化氢酶、过氧化物酶和超氧化物歧化酶活性，并在易感柑橘品种上诱导明显较少的坏死病变。skn7 突变体表现出介于 hsk1 和 hog1 突变株之间的杀菌剂抗性。skn7/hog1 双突变体表现出与具有单个 AaHSK1 基因突变的菌株相似的杀菌剂抗性。此外，A. alternata SKN7 在分生孢子形成中起作用。skn7 突变体产生的分生孢子比野生型产生的分生孢子更小，并且横隔膜更少。通过在内源启动子控制下引入和表达野生型 SKN7，突变体中的所有改变的表型都得到了恢复。
