Potato NPH3/RPT2-Like Protein StNRL1, Targeted by a Phytophthora infestans RXLR Effector, Is a Susceptibility Factor.

Plant pathogens deliver effectors to manipulate host processes. We know little about how fungal and oomycete effectors target host proteins to promote susceptibility, yet such knowledge is vital to understand crop disease. We show that either transient expression in Nicotiana benthamiana, or stable transgenic expression in potato (Solanum tuberosum), of the Phytophthora infestans RXLR effector Pi02860 enhances leaf colonization by the pathogen. Expression of Pi02860 also attenuates cell death triggered by the P. infestans microbe-associated molecular pattern INF1, indicating that the effector suppresses pattern-triggered immunity. However, the effector does not attenuate cell death triggered by Cf4/Avr4 coexpression, showing that it does not suppress all cell death activated by cell surface receptors. Pi02860 interacts in yeast two-hybrid assays with potato NPH3/RPT2-LIKE1 (NRL1), a predicted CULLIN3-associated ubiquitin E3 ligase. Interaction of Pi02860 in planta was confirmed by coimmunoprecipitation and bimolecular fluorescence complementation assays. Virus-induced gene silencing of NRL1 in N. benthamiana resulted in reduced P. infestans colonization and accelerated INF1-mediated cell death, indicating that this host protein acts as a negative regulator of immunity. Moreover, whereas NRL1 virus-induced gene silencing had no effect on the ability of the P. infestans effector Avr3a to suppress INF1-mediated cell death, such suppression by Pi02860 was significantly attenuated, indicating that this activity of Pi02860 is mediated by NRL1. Transient overexpression of NRL1 resulted in the suppression of INF1-mediated cell death and enhanced P. infestans leaf colonization, demonstrating that NRL1 acts as a susceptibility factor to promote late blight disease.

De novo pyrimidine biosynthesis in the oomycete plant pathogen Phytophthora infestans.

The oomycete Phytophthora infestans, causal agent of the tomato and potato late blight, generates important economic and environmental losses worldwide. As current control strategies are becoming less effective, there is a need for studies on oomycete metabolism to help identify promising and more effective targets for chemical control. The pyrimidine pathways are attractive metabolic targets to combat tumors, virus and parasitic diseases but have not yet been studied in Phytophthora. Pyrimidines are involved in several critical cellular processes and play structural, metabolic and regulatory functions. Here, we used genomic and transcriptomic information to survey the pyrimidine metabolism during the P. infestans life cycle. After assessing the putative gene machinery for pyrimidine salvage and de novo synthesis, we inferred genealogies for each enzymatic domain in the latter pathway, which displayed a mosaic origin. The last two enzymes of the pathway, orotate phosphoribosyltransferase and orotidine-5-monophosphate decarboxylase, are fused in a multi-domain enzyme and are duplicated in some P. infestans strains. Two splice variants of the third gene (dihydroorotase) were identified, one of them encoding a premature stop codon generating a non-functional truncated protein. Relative expression profiles of pyrimidine biosynthesis genes were evaluated by qRT-PCR during infection in Solanum phureja. The third and fifth genes involved in this pathway showed high up-regulation during biotrophic stages and down-regulation during necrotrophy, whereas the uracil phosphoribosyl transferase gene involved in pyrimidine salvage showed the inverse behavior. These findings suggest the importance of de novo pyrimidine biosynthesis during the fast replicative early infection stages and highlight the dynamics of the metabolism associated with the hemibiotrophic life style of pathogen.

Computational models in plant-pathogen interactions: the case of Phytophthora infestans.

BACKGROUND: Phytophthora infestans is a devastating oomycete pathogen of potato production worldwide. This review explores the use of computational models for studying the molecular interactions between P. infestans and one of its hosts, Solanum tuberosum. MODELING AND CONCLUSION: Deterministic logistics models have been widely used to study pathogenicity mechanisms since the early 1950s, and have focused on processes at higher biological resolution levels. In recent years, owing to the availability of high throughput biological data and computational resources, interest in stochastic modeling of plant-pathogen interactions has grown. Stochastic models better reflect the behavior of biological systems. Most modern approaches to plant pathology modeling require molecular kinetics information. Unfortunately, this information is not available for many plant pathogens, including P. infestans. Boolean formalism has compensated for the lack of kinetics; this is especially the case where comparative genomics, protein-protein interactions and differential gene expression are the most common data resources.