Rolke Yvonne, Tudzynski Paul
Institut für Botanik, Westf. Wilhelms-Universität Münster, Schlossgarten 3, D-48149 Münster, Germany.
Mol Microbiol. 2008 Apr;68(2):405-23. doi: 10.1111/j.1365-2958.2008.06159.x. Epub 2008 Feb 19.
Claviceps purpurea, the ergot fungus, is a highly specialized pathogen of grasses; its colonization of host ovarian tissue requires an extended period of strictly polarized, oriented growth towards the vascular tissue. To understand this process, we study the role of signalling factors affecting polarity and differentiation. We showed that the small GTPase Cdc42 is involved in polarity, sporulation and in planta growth in C. purpurea. Here we present evidence that the GTPase Rac has an even stronger and, in some aspects, inverse impact on growth and development: Deltarac mutants form coralline-like colonies, show hyper-branching, loss of polarity, sporulation and ability to penetrate. Functional analyses and yeast two-hybrid studies prove that the p21-activated kinase Cla4 is a major downstream partner of Rac. Phosphorylation assays of MAP kinases and expression studies of genes encoding reactive oxygen species (ROS)-scavenging and -generating enzymes indicate a function of Rac and Cla4 in fungal ROS homoeostasis which could contribute to their drastic impact on differentiation.
麦角菌（Claviceps purpurea）是一种高度特化的禾本科病原菌；它在宿主卵巢组织中的定殖需要一段长时间的严格极化、朝着维管组织定向生长的过程。为了解这一过程，我们研究了影响极性和分化的信号因子的作用。我们发现小GTP酶Cdc42参与了麦角菌的极性、孢子形成和植物体内生长。在此我们提供证据表明GTP酶Rac对生长和发育具有更强且在某些方面相反的影响：Rac缺失突变体形成珊瑚状菌落，表现出过度分支、极性丧失、孢子形成及穿透能力丧失。功能分析和酵母双杂交研究证明p21激活激酶Cla4是Rac的主要下游伙伴。丝裂原活化蛋白激酶的磷酸化分析以及编码活性氧（ROS）清除和产生酶的基因的表达研究表明Rac和Cla4在真菌ROS稳态中发挥作用，这可能是它们对分化产生巨大影响的原因。
