Journal
MOLECULAR PLANT-MICROBE INTERACTIONS
Volume 15, Issue 9, Pages 907-921Publisher
AMER PHYTOPATHOLOGICAL SOC
DOI: 10.1094/MPMI.2002.15.9.907
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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 oo-mycete 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. R cinnamomi pg gene sequences were expressed in PG-deficient yeast and found to confer PG activity, thereby confirming their functional identity. The predicted mature R 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 R cinnamomi PGs revealed a closer relationship with PGs from true fungi than with those from plants.
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