Improving -Mediated Genetic Transformation for Gene Function Studies and Mutagenesis in Cucumber ( L.).

In the post-genomics era, -mediated genetic transformation is becoming an increasingly indispensable tool for characterization of gene functions and crop improvement in cucumber ( L.). However, cucumber transformation efficiency is still low. In this study, we evaluated the effects of several key factors affecting the shoot-regeneration rate and overall transformation efficiency in cucumber including genotypes, the age and sources of explants, strains, infection/co-cultivation conditions, and selective agents. We showed that in general, North China cucumbers exhibited higher shoot-regeneration rate than US pickling or slicing cucumbers. The subapical ground meristematic regions from cotyledons or the hypocotyl had a similar shoot-regeneration efficiency that was also affected by the age of the explants. Transformation with the strain AGL1 yielded a higher frequency of positive transformants than with GV3101. The antibiotic kanamycin was effective in selection against non-transformants or chimeras. Optimization of various factors was exemplified with the development of transgenic plants overexpressing the () gene or RNAi of the gene in three cucumber lines. The streamlined protocol was also tested in transgenic studies in three additional genes. The overall transformation efficiency defined by the number of verified transgenic plants out of the number of seeds across multiple experiments was 0.2-1.7%. Screening among T OE transgenic plants identified novel, inheritable mutants for leaf or fruit color or size/shape, suggesting T-DNA insertion as a potential source of mutagenesis. The -mediated transformation protocol from this study could be used as the baseline for further improvements in cucumber transformation.