Quillaja genus (Quillajaceae family) is endemic to South America, where is represented by two species, Quillaja saponaria and Quillaja brasiliensis. One outstanding characteristic of these forest tree species is their production of saponins, a family of amphipathic glycosides, involved in the defensive response of plants against biotic and abiotic factors. Saponins are metabolites of economic importance due to their chemical and physical properties. Basic and applied research efforts performed during the last decades, mainly on Q. saponaria, have placed these compounds as an important raw material in industrial areas, such as food and beverage, cosmetics, vaccine production, biopesticides, among others. In this review, we summarize information on saponins from Quillaja species during the last years, analyzing current developments by application areas, as well as their chemical composition and properties. We also describe the general advances in revealing saponin biosynthesis pathways, related genes and Quillaja genomes, as well as the conservation status, domestication processes, and perspectives in the context of implementing genetic improvement programs.

Black cottonwood (Populus trichocarpa) is a species of economic interest and an outstanding study model. The aspen borer (Saperda calcarata) causes irreversible damage to poplars and other riparian species in North America. The insect can produce multiple effects ranging from the presence of some galleries in the stem to tree death. Despite the ecological and commercial importance of this tree–insect interaction, the genetic mechanisms underlying the response of P. trichocarpa to S. calcarata are scarcely understood. In this study, a common garden trial of P. trichocarpa provenances, established in Davis, California, was assessed at the second year of growth, regarding the infestation of S. calcarata from a natural outbreak. A genome-wide association study (GWAS) was conducted using 629k of exonic SNPs to assess the relationship between genomic variation and insect attack. Tree architecture, in terms of stem number per plant, and the wood metabolome were also included. Insect attack was independent of the number of stems per tree. The performed GWAS identified three significantly associated SNP markers (q-value < 0.2) belonging to the same number of gene models, encoding proteins involved in signal transduction mechanisms and secondary metabolite production, including that of R-mandelonitrile lyase, Chromodomain-helicase-DNA-binding family protein, and Leucine-rich repeat protein. These results are aligned with the current knowledge of defensive pathways in plants and trees, helping to expand the understanding of the defensive response mechanisms of black cottonwood against wood borer insects.