Stress biology and interactions between Solanum species and Phytophthora infestans

Stress biology and interactions between Solanum species and Phytophthora infestans-Studies in laboratory and field conditions Abstract Phytophthora infestans is a highly destructive pathogen in potato production. Developing potato cultivars with resistance against the pathogen is considered the most sustainable solution to address the problem. Wild Solanum species are a source of genes conferring resistance to P. infestans (Rpi-genes); however, the Solanum species genepool from Europe remains untapped. Since the pathogen can overcome host resistance, it is crucial to also consider alternative ways to enhance basal defence using resistance-inducers. Improving the knowledge base of Solanum - Phytophthora interactions, as well as unravelling possible effects of the interactions on other microbes and herbivores, can facilitate the use of host resistance to reduce yield losses. Furthermore, understanding plant innate immunity activation and the response to stress of host plants growing in field conditions can increase the efficiency of future disease control efforts. Characterization of the resistance against P. infestans in the three wild Solanum species growing in Sweden showed that S. nigrum is resistant and S. physalifolium is susceptible whereas there was large resistance variation among S. dulcamara accessions. A study of S. physalifoilum showed direct and transgenerational BABA-induced resistance against P. infestans. To further understand the molecular basis of these interactions, a transcriptome comparison based on RNA-seq data was performed in the three wild Solanum species and three potato clones with varying resistance level to the pathogen, after inoculation with P. infestans. The transcriptome analysis identified expanded or depleted transcript families which are associated with resistance. It also retrieved host R-gene like sequences and possible pathogenicity factors produced by the pathogen during the infection process. Moreover, a tritrophic interaction study showed that a generalist moth (Spodoptera littoralis) prefers to oviposit on a susceptible potato clone inoculated with P. infestans compared to uninoculated control plants as well as inoculated resistant clone. Introduction of a resistance gene from a wild Solanum species into potato can reduce the effects of P. infestans as well as S. littoralis. To understand the prevalence of innate immunity activation in agriculture and nature, more than 500 apoplastic leaf samples isolated from S. nigrum and S. dulcamara growing in natural populations as well as from five potato cultivars with varying levels of resistance to P. infestans were analysed for the presence of PR proteins. The results showed that only one third of the plants have the innate immunity activated. Presence of PR proteins increases towards the end of the growing season, which may be is linked to an increased presence of natural enemies. Moreover, we performed apoplastic proteome analysis, using label free quantitative proteomics and activity based protein profiling (ABPP) in order to get overview of involved processes. We found that most of the proteins with increased abundance in the field compared to in greenhouse condition were related to biotic stress response. ABPP also showed differential activity statuses of serine hydrolases and β-glucosidases in field and greenhouse growing conditions. Furthermore, the activity of serine hydrolases and β-glucosidases varies across the growing season within the same field. Non-plastic peptide biomarkers for potato stress response were suggested. Keywords: Solanum, P. infestans, Rpi-genes, BABA, tritrophic, apoplast, quantitative proteomics, ABPP, Biomarkers Author’s address: Kibrom Berhe Abreha, SLU, Department of Plant Protection Biology, P.O. Box 102, 230 53 Alnarp, Sweden E-mail: Kibrom.abreha@slu.se