Opalski Krystina S, Schultheiss Holger, Kogel Karl-Heinz, Hückelhoven Ralph
Institute of Phytopathology and Applied Zoology, Justus-Liebig-University Giessen, Heinrich-Buff Ring 26-32, D-35392 Giessen, Germany.
Plant J. 2005 Jan;41(2):291-303. doi: 10.1111/j.1365-313X.2004.02292.x.
Cytoskeleton remodelling is a crucial process in determining the polarity of dividing and growing plant cells, as well as during interactions with the environment. Nothing is currently known about the proteins, which regulate actin remodelling during interactions with invading pathogens. The biotrophic powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) invades susceptible barley (Hordeum vulgare L.) by penetrating epidermal cells, which remain intact during fungal development. In contrast, resistant host plants prevent infection by inhibiting penetration through apoplastic mechanisms, which require focusing defence reactions on the site of attack. We stained actin filaments in a susceptible Mlo-genotype and a near-isogenic race-non-specifically resistant barley mlo5-mutant genotype using fluorescence-labelled phalloidin after chemical fixation. This revealed that the actin cytoskeleton is differentially reorganized in susceptible and resistant hosts challenged by Bgh. Actin filaments were polarized towards the sites of attempted penetration in the resistant host, whereas when susceptible hosts were penetrated, a more subtle reorganization took place around fungal haustoria. Strong actin filament focusing towards sites of fungal attack was closely associated with successful prevention of penetration. Actin focusing was less frequent and seemingly delayed in susceptible wild-type barley expressing the susceptibility factor MLO. Additionally, single cell overexpression of a constitutively activated RAC/ROP G-protein, CA RACB, another potential host susceptibility factor and hypothetical actin cytoskeleton regulator, partly inhibited actin reorganization when under attack from Bgh, whereas knockdown of RACB promoted actin focusing. We conclude that RACB and, potentially, MLO are host proteins involved in the modulation of actin reorganization and cell polarity in the interaction of barley with Bgh.
细胞骨架重塑是决定植物分裂和生长细胞极性的关键过程，在与环境相互作用时也是如此。目前对于在与入侵病原体相互作用期间调节肌动蛋白重塑的蛋白质尚不清楚。活体营养型白粉病菌禾本科布氏白粉菌大麦专化型（Bgh）通过穿透表皮细胞侵入感病大麦（大麦），在真菌发育过程中表皮细胞保持完整。相比之下，抗性寄主植物通过抑制穿透的质外体机制来阻止感染，这需要将防御反应集中在攻击部位。我们在化学固定后，使用荧光标记的鬼笔环肽对感病的Mlo基因型和近等基因系种族非特异性抗性大麦mlo5突变体基因型中的肌动蛋白丝进行染色。这表明，在受到Bgh攻击的感病和抗性寄主中，肌动蛋白细胞骨架发生了不同的重组。在抗性寄主中，肌动蛋白丝向试图穿透的部位极化，而当感病寄主被穿透时，在真菌吸器周围发生了更细微的重组。强烈的肌动蛋白丝集中在真菌攻击部位与成功阻止穿透密切相关。在表达感病因子MLO的感病野生型大麦中，肌动蛋白集中现象较少且似乎延迟。此外，组成型激活的RAC/ROP G蛋白CA RACB（另一种潜在的寄主感病因子和假定的肌动蛋白细胞骨架调节因子）的单细胞过表达，在受到Bgh攻击时部分抑制了肌动蛋白重组，而RACB的敲低则促进了肌动蛋白集中。我们得出结论，RACB以及可能的MLO是参与调节大麦与Bgh相互作用中肌动蛋白重组和细胞极性的寄主蛋白。
