Division of Plant Science, Research School of Biology, College of Medicine, Biology, and Environment, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
Plant Cell. 2010 Jun;22(6):2017-32. doi: 10.1105/tpc.109.072983. Epub 2010 Jun 4.
Translocation of pathogen effector proteins into the host cell cytoplasm is a key determinant for the pathogenicity of many bacterial and oomycete plant pathogens. A number of secreted fungal avirulence (Avr) proteins are also inferred to be delivered into host cells, based on their intracellular recognition by host resistance proteins, including those of flax rust (Melampsora lini). Here, we show by immunolocalization that the flax rust AvrM protein is secreted from haustoria during infection and accumulates in the haustorial wall. Five days after inoculation, the AvrM protein was also detected within the cytoplasm of a proportion of plant cells containing haustoria, confirming its delivery into host cells during infection. Transient expression of secreted AvrL567 and AvrM proteins fused to cerulean fluorescent protein in tobacco (Nicotiana tabacum) and flax cells resulted in intracellular accumulation of the fusion proteins. The rust Avr protein signal peptides were functional in plants and efficiently directed fused cerulean into the secretory pathway. Thus, these secreted effectors are internalized into the plant cell cytosol in the absence of the pathogen, suggesting that they do not require a pathogen-encoded transport mechanism. Uptake of these proteins is dependent on signals in their N-terminal regions, but the primary sequence features of these uptake regions are not conserved between different rust effectors.
病原体效应蛋白向宿主细胞质的易位是许多细菌和卵菌植物病原体致病性的关键决定因素。许多分泌的真菌无毒（Avr）蛋白也被推断为通过宿主抗性蛋白进入宿主细胞，包括亚麻锈菌（Melampsora lini）的抗性蛋白。在这里，我们通过免疫定位显示，亚麻锈菌 AvrM 蛋白在感染期间从吸器中分泌，并在吸器壁中积累。接种后 5 天，在含有吸器的部分植物细胞的细胞质中也检测到了 AvrM 蛋白，证实了其在感染过程中被递送到宿主细胞中。在烟草（Nicotiana tabacum）和亚麻细胞中瞬时表达与天蓝色荧光蛋白融合的分泌型 AvrL567 和 AvrM 蛋白，导致融合蛋白在细胞内积累。锈菌 Avr 蛋白信号肽在植物中具有功能，并能有效地将融合的天蓝色导向分泌途径。因此，这些分泌的效应子在没有病原体的情况下被内化到植物细胞胞质溶胶中，这表明它们不需要病原体编码的运输机制。这些蛋白的摄取依赖于其 N 端区域的信号，但不同锈菌效应子之间这些摄取区域的主要序列特征并不保守。
