Chen Changbin, Harel Arye, Gorovoits Rena, Yarden Oded, Dickman Martin B
Department of Plant Pathology, 406 Plant Sciences Hall, University of Nebraska-Lincoln, 68583-0722, USA.
Mol Plant Microbe Interact. 2004 Apr;17(4):404-13. doi: 10.1094/MPMI.2004.17.4.404.
Sclerotial development is fundamental to the disease cycle of the omnivorous broad host range fungal phytopathogen Sclerotinia sclerotiorum. We have isolated a highly conserved homolog of ERK-type mitogen-activated protein kinases (MAPKs) from S. sclerotiorum (Smk1) and have demonstrated that Smk1 is required for sclerotial development. The smk1 transcription and MAPK enzyme activity are induced dramatically during sclerotiogenesis, especially during the production of sclerotial initials. When PD98059 (a specific inhibitor of the activation of MAPK by MAPK kinase) was applied to differentiating cultures or when antisense expression of smk1 was induced, sclerotial maturation was impaired. The smk1 transcript levels were highest under acidic pH conditions, suggesting that Smk1 regulates sclerotial development via a pH-dependent signaling pathway, involving the accumulation of oxalic acid, a previously identified pathogenicity factor that functions at least in part by reducing pH. Addition of cyclic AMP (cAMP) inhibited smk1 transcription, MAPK activation, and sclerotial development. Thus, S. sclerotiorum can coordinate environmental signals (such as pH) to trigger a signaling pathway mediated by Smk1 to induce sclerotia formation, and this pathway is negatively regulated by cAMP.
菌核发育是多食性广寄主范围真菌植物病原菌核盘菌病害循环的基础。我们从核盘菌中分离出一种高度保守的ERK型丝裂原活化蛋白激酶（MAPK）同源物（Smk1），并证明Smk1是菌核发育所必需的。在菌核形成过程中，尤其是在菌核初始形成期间，Smk1转录和MAPK酶活性会显著诱导。当将PD98059（一种MAPK激酶激活MAPK的特异性抑制剂）应用于分化培养物或诱导smk1的反义表达时，菌核成熟受到损害。Smk1转录水平在酸性pH条件下最高，这表明Smk1通过pH依赖性信号通路调节菌核发育，该通路涉及草酸的积累，草酸是一种先前确定的致病因子，其至少部分通过降低pH发挥作用。添加环磷酸腺苷（cAMP）会抑制smk1转录、MAPK激活和菌核发育。因此，核盘菌可以协调环境信号（如pH）以触发由Smk1介导的信号通路来诱导菌核形成，并且该通路受到cAMP的负调控。
