Understanding the Impact of Plant Nutrition on Plant-Oomycete Interactions

Plants are surrounded by various threats from the environment such as pathogens, abiotic stresses, and animal attacks. Nutrient content and distribution are essential for plant growth and development as well as plant immunity. Pathogens extract nutrients from host plants to benefit their own growth and reproduction. Sulfate, amino acids, and phosphate are indispensable elements for plant growth, plant nutrition, and plant resistance/susceptibility to disease. However, the role of these nutrients in plant-oomycete interactions is an unexplored area. We developed a hydroponic system to precisely control the nutrients applied to plants. We used Arabidopsis thaliana and Nicotiana benthamiana (N. b) as model plants. Hyaloperonospora arabidopsidis as well as two Phytophthora species, Phytophothora capsici (P. cap) and Phytophothora nicotianae (P. nic) were used as model oomycete pathogens. Hpa is an obligate biotrophic pathogen that obtains nutrients directly from the host plant without causing cell death, while P. cap and P. nic are hemibiotrophic pathogens that display a biotrophic phase followed by a necrotrophic phase where they feed on dead cells. Genomic evidence suggests that these pathogens might obtain nutrients including sulfur in different forms from the host (organic and inorganic respectively). We have optimized the hydroponic system and used Taqman PCR assays and sporangiophore counts to assay the influence of sulfur nutrients on Hpa and P. cap infections. We found that (1) sulfur transporter and metabolism genes play essential roles in plant-oomycete interactions; (2) sulfur is critical components for HR responses against Hpa; (3) low sulfur induces pathogenesis related genes as a systemic acquired response. RNA-seq analysis on Phytophthora-infected Arabidopsis suggested that sulfur transport, assimilation, and metabolism play an important role in plant-oomycete interactions. A second project used RNA-seq analysis on P. nic infected N. b, to identify potential nutrition-related-plant genes that are necessary for full pathogen virulence. RNAi knockdowns of N. b AAP6 (amino acid permease 6) and PHT4 (phosphate transporter 4) genes showed an inhibition of oomycete colonization. These experiments together advance the study on the interplay between nutrient assimilation/metabolism in host plants and oomycete infection which will provide insight into the mechanisms how pathogens intercept nutrients from host. In the long-term, this research could reveal new traits applicable for disease resistance to promote crop and food production.