Damasceno Cynthia M B, Bishop John G, Ripoll Daniel R, Win Joe, Kamoun Sophien, Rose Jocelyn K C
Department of Plant Biology, Cornell University, Ithaca, NY 14853, U.S.A.
Mol Plant Microbe Interact. 2008 Jun;21(6):820-30. doi: 10.1094/MPMI-21-6-0820.
During invasion of their plant hosts, species of the oomycete genus Phytophthora secrete glucanase inhibitor proteins (GIPs) into the plant apoplast, which bind and inhibit the activity of plant extracellular endo-beta-1,3-glucanases (EGases). GIPs show structural homology to the chymotrypsin class of serine proteases (SP) but lack proteolytic activity due to the absence of an intact catalytic triad and, thus, belong to a broader class of proteins called serine protease homologs (SPH). To study the evolutionary relationship between GIPs and functional SP, database searches were used to identify 48 GIP homologs in the P. sojae, P. ramorum, and P. infestans genomes, composing GIPs, SPH, and potentially functional SP. Analyses of P. infestans-inoculated tomato leaves showed that P. infestans GIPs and tomato EGases are present in the apoplast and form stable complexes in planta. Studies of the temporal expression of a four-membered GIP family from P. infestans (PiGIP1 to PiGIP4) further revealed that the genes show distinctly different patterns during an infection timecourse. Codon evolution analyses of GIP homologs identified several positively selected peptide sites and structural modeling revealed them to be in close proximity to rapidly evolving EGase residues, suggesting that the interaction between GIPs and EGases has the hallmarks of a coevolving molecular arms race.
在疫霉属（Phytophthora）物种侵染其植物宿主的过程中，它们会向植物质外体分泌葡聚糖酶抑制蛋白（GIPs），这些蛋白会结合并抑制植物细胞外内切-β-1,3-葡聚糖酶（EGases）的活性。GIPs与丝氨酸蛋白酶（SP）的胰凝乳蛋白酶类具有结构同源性，但由于缺乏完整的催化三联体而缺乏蛋白水解活性，因此属于一类更广泛的蛋白质，称为丝氨酸蛋白酶同源物（SPH）。为了研究GIPs与功能性SP之间的进化关系，通过数据库搜索在大豆疫霉（P. sojae）、栎叶疫霉（P. ramorum）和致病疫霉（P. infestans）的基因组中鉴定出48个GIP同源物，包括GIPs、SPH和潜在的功能性SP。对接种致病疫霉的番茄叶片的分析表明，致病疫霉GIPs和番茄EGases存在于质外体中，并在植物体内形成稳定的复合物。对致病疫霉的一个由四个成员组成的GIP家族（PiGIP1至PiGIP4）的时间表达研究进一步表明，这些基因在感染过程中表现出明显不同的模式。GIP同源物的密码子进化分析确定了几个正选择的肽位点，结构建模显示它们紧邻快速进化的EGase残基，这表明GIPs与EGases之间的相互作用具有协同进化的分子军备竞赛的特征。
