Transgenic expression of Hyp-1 gene from Hypericum perforatum L. alters expression of defense-related genes and modulates recalcitrance to Agrobacterium tumefaciens

Hypericum perforatum L. is a reservoir of high-value secondary metabolites of increasing interest to researchers and to the pharmaceutical industry. However, improving their production via genetic manipulation is a challenging task, as H. perforatum is recalcitrant to Agrobacterium tumefaciens-mediated transformation. Here, phenolic oxidative coupling protein (Hyp-1), a pathogenesis-related (PR) class 10 family gene, was selected from a subtractive cDNA library from A. tumefaciens-treated H. perforatum suspension cells. The role of Hyp-1 in defense against A. tumefaciens was analyzed in transgenic Nicotiana tabacum and Lactuca sativa overexpressing Hyp-1, and in Catharanthus roseus silenced for its homologous Hyp-1 gene, CrIPR. Results showed that Agrobacterium-mediated expression efficiency greatly decreased in Hyp-1 transgenic plants. However, silencing of CrIPR induced CrPR-5 expression and decreased expression efficiency of Agrobacterium. The expression of core genes involved in several defense pathways was also analyzed in Hyp-1 transgenic tobacco plants. Overexpression of Hyp-1 led to an ample down-regulation of key genes involved in auxin signaling, microRNA-based gene silencing, detoxification of reactive oxygen species, phenylpropanoid pathway and PRs. Moreover, Hyp-1 was detected in the nucleus, plasma membrane and the cytoplasm of epidermal cells by confocal microscopy. Overall, our findings suggest Hyp-1 modulates recalcitrance to A. tumefaciens-mediated transformation in H. perforatum.