Identification of Late Blight Resistance-Related Metabolites and Genes in Potato through Nontargeted Metabolomics

Late blight of potato (Solanum tuberosum) caused by Phytophthora infestans significantly reduces the productivity of potato around the world. Resistance to late blight in potato is either qualitative or quantitative. Qualitative resistance governed by race-specific single R genes is well characterized and gives complete resistance, but is not durable. Quantitative resistance governed by polygenes gives partial resistance, but is durable in nature. However, the quantitative resistance mechanisms are poorly studied and are not efficiently exploited in potato breeding. A nontargeted metabolic profiling of resistant (F06037) and susceptible (Shepody) potato cultivars, using high-resolution liquid chromatography-mass spectrometry, was applied to elucidate the quantitative resistance mechanisms against P. infestans (US-8 genotype). The hydroxycinnamic acid amides (HCAAs) of the shunt phenylpropanoid pathway were highly induced following pathogen inoculation in F06037. In parallel, the transcript abundances of genes that catalyze the biosynthesis of these metabolites, such as 4-coumarate:CoA ligase, tyrosine decarboxylase, ornithine decarboxylase, tyramine hydroxycinnamoyl transferase, and putrescine hydroxycinnamoyl transferase, were also higher in the resistant genotype. Sequencing of the coding genes of these enzymes revealed single-nucleotide polymorphisms between resistant and susceptible genotypes, and the amino acid changes caused missense mutations altering protein functions. HCAAs deposited at host cell walls inhibit pathogen colonization, thus reducing lesion expansion. In addition, these also act as phytoalexins, leading to the reduced biomass of the pathogen. Following validation, the HCAAs can be used as biomarker metabolites for late blight resistance. The putative candidate genes can be either used to develop allele-specific markers for marker-assisted breeding programs or suitably stacked into elite cultivars through cisgenic approaches, following validation.