The NLP toxin family in Phytophthora sojae includes rapidly evolving groups that lack necrosis-inducing activity.

Abstract

Necrosis- and ethylene-inducing-like proteins (NLP) are widely distributed in eukaryotic and prokaryotic plant pathogens and are considered to be important virulence factors. We identified, in total, 70 potential Phytophthora sojae NLP genes but 37 were designated as pseudogenes. Sequence alignment of the remaining 33 NLP delineated six groups. Three of these groups include proteins with an intact heptapeptide (Gly-His-Arg-His-Asp-Trp-Glu) motif, which is important for necrosis-inducing activity, whereas the motif is not conserved in the other groups. In total, 19 representative NLP genes were assessed for necrosis-inducing activity by heterologous expression in Nicotiana benthamiana. Surprisingly, only eight genes triggered cell death. The expression of the NLP genes in P. sojae was examined, distinguishing 20 expressed and 13 nonexpressed NLP genes. Real-time reverse-transcriptase polymerase chain reaction results indicate that most NLP are highly expressed during cyst germination and infection stages. Amino acid substitution ratios (Ka/Ks) of 33 NLP sequences from four different P. sojae strains resulted in identification of positive selection sites in a distinct NLP group. Overall, our study indicates that expansion and pseudogenization of the P. sojae NLP family results from an ongoing birth-and-death process, and that varying patterns of expression, necrosis-inducing activity, and positive selection suggest that NLP have diversified in function.

• Authors: Suomeng Dong, Guanghui Kong, Dinah Qutob, Xiaoli Yu, Junli Tang, Jixiong Kang, Tingting Dai, Hai Wang, Mark Gijzen, Yuanchao Wang
• Journal: Molecular plant-microbe interactions : MPMI (Mol Plant Microbe Interact) Vol. 25 Issue 7 Pg. 896-909 (Jul 2012) ISSN: 0894-0282 [Print] United States
• PMID: 22397404 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Amino Acid Motifs
• Amino Acid Sequence
• Amino Acid Substitution
• Base Sequence
• Gene Expression Regulation, Developmental (genetics)
• Gene Library
• Models, Molecular
• Molecular Sequence Data
• Multigene Family (genetics)
• Necrosis
• Phylogeny
• Phytophthora (genetics, metabolism, pathogenicity)
• Plant Diseases (parasitology)
• Pseudogenes
• Real-Time Polymerase Chain Reaction
• Sequence Alignment
• Sequence Analysis, DNA
• Tobacco (parasitology)