Bellafiore Stéphane, Shen Zhouxin, Rosso Marie-Noelle, Abad Pierre, Shih Patrick, Briggs Steven P
Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA.
PLoS Pathog. 2008 Oct;4(10):e1000192. doi: 10.1371/journal.ppat.1000192. Epub 2008 Oct 31.
The root knot nematode, Meloidogyne incognita, is an obligate parasite that causes significant damage to a broad range of host plants. Infection is associated with secretion of proteins surrounded by proliferating cells. Many parasites are known to secrete effectors that interfere with plant innate immunity, enabling infection to occur; they can also release pathogen-associated molecular patterns (PAMPs, e.g., flagellin) that trigger basal immunity through the nematode stylet into the plant cell. This leads to suppression of innate immunity and reprogramming of plant cells to form a feeding structure containing multinucleate giant cells. Effectors have generally been discovered using genetics or bioinformatics, but M. incognita is non-sexual and its genome sequence has not yet been reported. To partially overcome these limitations, we have used mass spectrometry to directly identify 486 proteins secreted by M. incognita. These proteins contain at least segmental sequence identity to those found in our 3 reference databases (published nematode proteins; unpublished M. incognita ESTs; published plant proteins). Several secreted proteins are homologous to plant proteins, which they may mimic, and they contain domains that suggest known effector functions (e.g., regulating the plant cell cycle or growth). Others have regulatory domains that could reprogram cells. Using in situ hybridization we observed that most secreted proteins were produced by the subventral glands, but we found that phasmids also secreted proteins. We annotated the functions of the secreted proteins and classified them according to roles they may play in the development of root knot disease. Our results show that parasite secretomes can be partially characterized without cognate genomic DNA sequence. We observed that the M. incognita secretome overlaps the reported secretome of mammalian parasitic nematodes (e.g., Brugia malayi), suggesting a common parasitic behavior and a possible conservation of function between metazoan parasites of plants and animals.
根结线虫（Meloidogyne incognita）是一种专性寄生虫，会对多种寄主植物造成严重损害。感染与增殖细胞周围分泌的蛋白质有关。已知许多寄生虫会分泌效应子来干扰植物的固有免疫，从而引发感染；它们还可以通过线虫口针向植物细胞释放能触发基础免疫的病原体相关分子模式（PAMPs，如鞭毛蛋白）。这会导致固有免疫受到抑制，植物细胞重新编程以形成包含多核巨细胞的取食结构。效应子通常是通过遗传学或生物信息学方法发现的，但南方根结线虫是无性繁殖的，其基因组序列尚未见报道。为了部分克服这些限制，我们使用质谱法直接鉴定了南方根结线虫分泌的486种蛋白质。这些蛋白质与我们的3个参考数据库（已发表的线虫蛋白质；未发表的南方根结线虫ESTs；已发表的植物蛋白质）中发现的蛋白质至少具有部分序列一致性。几种分泌蛋白与植物蛋白同源，它们可能会模拟植物蛋白，并且含有表明已知效应子功能的结构域（例如，调节植物细胞周期或生长）。其他蛋白具有可使细胞重新编程的调节结构域。通过原位杂交我们观察到，大多数分泌蛋白是由腹侧下腺产生的，但我们发现尾感器也能分泌蛋白质。我们注释了分泌蛋白的功能，并根据它们在根结病发展中可能发挥的作用进行了分类。我们的结果表明，在没有同源基因组DNA序列的情况下，也可以部分表征寄生虫的分泌组。我们观察到南方根结线虫的分泌组与已报道的哺乳动物寄生线虫（如马来布鲁线虫）的分泌组有重叠，这表明动植物的后生动物寄生虫之间存在共同的寄生行为和可能的功能保守性。
