Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
PLoS One. 2011;6(8):e23242. doi: 10.1371/journal.pone.0023242. Epub 2011 Aug 16.
Phytoplasmas are bacterial plant pathogens that have devastating effects on the yields of crops and plants worldwide. They are intracellular parasites of both plants and insects, and are spread among plants by insects. How phytoplasmas can adapt to two diverse environments is of considerable interest; however, the mechanisms enabling the "host switching" between plant and insect hosts are poorly understood. Here, we report that phytoplasmas dramatically alter their gene expression in response to "host switching" between plant and insect. We performed a detailed characterization of the dramatic change that occurs in the gene expression profile of Candidatus Phytoplasma asteris OY-M strain (approximately 33% of the genes change) upon host switching between plant and insect. The phytoplasma may use transporters, secreted proteins, and metabolic enzymes in a host-specific manner. As phytoplasmas reside within the host cell, the proteins secreted from phytoplasmas are thought to play crucial roles in the interplay between phytoplasmas and host cells. Our microarray analysis revealed that the expression of the gene encoding the secreted protein PAM486 was highly upregulated in the plant host, which is also observed by immunohistochemical analysis, suggesting that this protein functions mainly when the phytoplasma grows in the plant host. Additionally, phytoplasma growth in planta was partially suppressed by an inhibitor of the MscL osmotic channel that is highly expressed in the plant host, suggesting that the osmotic channel might play an important role in survival in the plant host. These results also suggest that the elucidation of "host switching" mechanism may contribute to the development of novel pest controls.
植原体是一种细菌性植物病原体，对全球农作物和植物的产量造成了毁灭性的影响。它们是植物和昆虫的细胞内寄生虫，通过昆虫在植物间传播。植原体如何适应两种截然不同的环境是一个非常有趣的问题；然而，对于使植物和昆虫宿主之间“宿主转换”的机制知之甚少。在这里，我们报告植原体在植物和昆虫之间的“宿主转换”过程中，其基因表达会发生显著改变。我们详细描述了在植物和昆虫之间宿主转换时，OY-M 菌株（约 33%的基因发生变化）的基因表达谱发生的剧烈变化。植原体可能以宿主特异性的方式使用转运蛋白、分泌蛋白和代谢酶。由于植原体存在于宿主细胞内，因此认为从植原体分泌的蛋白质在植原体和宿主细胞之间的相互作用中发挥着关键作用。我们的微阵列分析显示，编码分泌蛋白 PAM486 的基因在植物宿主中的表达高度上调，免疫组织化学分析也观察到这一点，表明该蛋白主要在植原体在植物宿主中生长时发挥作用。此外，在植物宿主中高度表达的 MscL 渗透通道抑制剂部分抑制了植原体在植物中的生长，表明该渗透通道可能在植物宿主中的存活中发挥重要作用。这些结果还表明，阐明“宿主转换”机制可能有助于开发新的害虫控制方法。
