Integrating metabolomics and targeted gene expression to uncover potential biomarkers of fungal/oomycetes-associated disease susceptibility in grapevine.

Vitis vinifera, one of the most cultivated fruit crops, is susceptible to several diseases particularly caused by fungus and oomycete pathogens. In contrast, other Vitis species (American, Asian) display different degrees of tolerance/resistance to these pathogens, being widely used in breeding programs to introgress resistance traits in elite V. vinifera cultivars. Secondary metabolites are important players in plant defence responses. Therefore, the characterization of the metabolic profiles associated with disease resistance and susceptibility traits in grapevine is a promising approach to identify trait-related biomarkers. In this work, the leaf metabolic composition of eleven Vitis genotypes was analysed using an untargeted metabolomics approach. A total of 190 putative metabolites were found to discriminate resistant/partial resistant from susceptible genotypes. The biological relevance of discriminative compounds was assessed by pathway analysis. Several compounds were selected as promising biomarkers and the expression of genes coding for enzymes associated with their metabolic pathways was analysed. Reference genes for these grapevine genotypes were established for normalisation of candidate gene expression. The leucoanthocyanidin reductase 2 gene (LAR2) presented a significant increase of expression in susceptible genotypes, in accordance with catechin accumulation in this analysis group. Up to our knowledge this is the first time that metabolic constitutive biomarkers are proposed, opening new insights into plant selection on breeding programs.

Genetic Relationships Among Portuguese Cultivated and Wild Vitis vinifera L. Germplasm.

The domesticated grapevine spread along the Mediterranean basin from the primary Near East domestication area, where the greatest genetic diversity is found in its ancestor, the wild vine populations. Portuguese wild populations are on the southwestern fringe of the distribution of the Vitis vinifera L. ssp. sylvestris (C.C. Gmel.) Hegi in Europe. During the last Glacial Period they became isolated from the previous continuum that had been the territory of wild vine populations. Archaeological remains of domesticated vinifera grapevines in Portugal date back from 795 Before Common Era (BCE) in the lower Tagus river basin. In this work, 258 Portuguese vinifera varieties and sylvestris plants were characterized using 261 single nucleotide polymorphism (SNP) markers. The study of the genetic diversity of this local germplasm, its population structure and kinship, all framed in their historical and geographical backgrounds, revealed a complex network of first-degree relationships, where only Iberian varieties are involved. Some Iberian genotypes, like Alfrocheiro (Bruñal, in Spain), Sarigo (Cayetana Blanca), Mourisco Branco (Hebén), Amaral (Caiño Bravo), and Marufo (Moravia Dulce) are ancestors of a considerable fraction of all the autochthonous analyzed varieties. A part of the diversity developed was mostly local in some cases as shown by the closeness of several varieties (Vinhos Verdes) to the wild cluster in different analyses. Besides, several evidences of introgression of domesticated germplasm into wild vines was found, substantiating the high risk of genetic contamination of the sylvestris subspecies. All these findings together to the known matching between the wild maternal lineage of the Iberian Peninsula and an important number of Portuguese grapevine varieties (chlorotype A), point out that some of these varieties derive, directly or indirectly, from originally local wild populations, supporting the possible occurrence of secondary events of local domestication, or, at least, of an introgression process of wild into cultivated grapevines.