Overexpression of Ginkbilobin-2 homologous domain gene improves tolerance to Phytophthora cinnamomi in somatic embryos of Quercus suber

In recent decades an extensive mortality and decline of Quercus suber populations mainly caused by Phytophthora cinnamomi has been observed. In the current study, a chestnut gene homologous to ginkbilobin-2 (Cast_Gnk2-like), which in Ginkgo biloba codifies an antifungal protein, was transferred into cork oak somatic embryos of three different embryogenic lines by Agrobacterium mediated transformation. The transformation efficiency varied on the genotype from 2.5 to 9.2%, and a total of 22 independent transformed lines were obtained. The presence of Cast_Gnk2-like gene in transgenic embryos was verified in all lines by PCR. The number of transgene copies was estimated by qPCR in embryogenic lines with high proliferation ability and it varied between 1 and 5. In addition, the expression levels of Cast_Gnk2-like gene were determined in the embryogenic lines, with higher levels in lines derived from the genotype ALM6-WT. Transgenic plants were obtained from all transgenic lines and evaluated after cold storage of the somatic embryos for 2 months and subsequent transfer to germination medium. In vitro tolerance tests made under controlled conditions and following zoospore treatment showed that plants overexpressing Cast_Gnk2-like gene improved tolerance against Pc when compared to wild type ones.