Götesson Arvid, Marshall Jerry S, Jones David A, Hardham Adrienne R
Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra ACT.
Mol Plant Microbe Interact. 2002 Sep;15(9):907-21. doi: 10.1094/MPMI.2002.15.9.907.
Polygalacturonases (PGs) are secreted by fungal pathogens during saprophytic and parasitic growth, and their degradation of pectin in the plant cell wall is believed to play a major role in tissue invasion and maceration. In this study, PG activity was demonstrated in culture filtrates of the oomycete plant pathogen, Phytophthora cinnamomi. A P. cinnamomi pg gene fragment amplified using degenerate primers based on conserved regions in fungal and plant PGs was used to isolate 17 complete P. cinnamomi pg genes and pseudogenes from a genomic library and partial sequence for another two genes. Gel blotting of genomic DNA indicated that there may be even more pg genes in the P. cinnamomi genome. P. cinnamomi pg gene sequences were expressed in PG-deficient yeast and found to confer PG activity, thereby confirming their functional identity. The predicted mature P. cinnamomi PGs fall into subgroups that exhibit large differences in the extent of N-glycosylation, isoelectric points, and N- and C-terminal structure. Evidence for birth-and-death and reticulate evolution in the P. cinnamomi pg gene family was obtained, and some codons for surface exposed residues in the P. cinnamomi PGs were shown to have been subject to diversifying selection. Contrary to accepted phylogenies for other proteins, phylogenetic analysis of the P. cinnamomi PGs revealed a closer relationship with PGs from true fungi than with those from plants.
多聚半乳糖醛酸酶（PGs）在真菌病原体腐生和寄生生长过程中分泌，据信它们对植物细胞壁中果胶的降解在组织侵染和浸解中起主要作用。在本研究中，卵菌植物病原体樟疫霉的培养滤液中证实了PG活性。使用基于真菌和植物PGs保守区域的简并引物扩增得到的樟疫霉pg基因片段，用于从基因组文库中分离出17个完整的樟疫霉pg基因和假基因，以及另外两个基因的部分序列。基因组DNA的凝胶印迹表明樟疫霉基因组中可能存在更多的pg基因。樟疫霉pg基因序列在缺乏PG的酵母中表达，并被发现具有PG活性，从而证实了它们的功能特性。预测的成熟樟疫霉PGs分为不同的亚组，这些亚组在N-糖基化程度、等电点以及N端和C端结构方面表现出很大差异。获得了樟疫霉pg基因家族中生死进化和网状进化的证据，并且樟疫霉PGs中一些表面暴露残基的密码子显示受到多样化选择。与其他蛋白质公认的系统发育不同，樟疫霉PGs的系统发育分析表明，它们与真正真菌的PGs的关系比与植物的PGs更密切。
