Agrobacterium-Mediated) Transformation of Cucumber (Cucumis SativusL.) and Plant Regeneration

Recent Progress in the Regeneration and Genetic Transformation System of Cucumber

Cucumber (Cucumis sativus L.), belonging to the gourd family (Cucurbitaceae), is one of the major vegetable crops in China. Conventional genetic breeding methods are ineffective for improving the tolerance of cucumber to various environmental stresses, diseases, and pests in the short term, but bio-engineering technologies can be applied to cucumber breeding to produce new cultivars with high yield and quality. Regeneration and genetic transformation systems are key technologies in modern cucumber breeding. Compared with regeneration systems, genetic transformation systems are not yet fully effective, and the low efficiency of genetic transformation is a bottleneck in cucumber cultivation. Here, we systematically review the key factors influencing the regeneration and genetic transformation of cucumber plants, including the selection of genotype, source of explants and forms of exogenous hormones added to the medium, the methods of transgene introduction and co-cultivation, and selection methods. In addition, we also focus on recent advances in the study of molecular mechanisms underlying important agronomic traits using genetic transformation technology, such as fruit length, fruit warts, and floral development. This review provides reference information for future research on improvements in cucumber varieties.

Targeted creating new mutants with compact plant architecture using CRISPR/Cas9 genome editing by an optimized genetic transformation procedure in cucurbit plants

Fruits and vegetables in the Cucurbitaceae family contribute greatly to the human diet, for example, cucumber, melon, watermelon and squash. The widespread use of genome editing technologies has greatly accelerated the functional characterization of genes as well as crop improvement. However, most economically important cucurbit plants, including melon and squash, remain recalcitrant to standard Agrobacterium tumefaciens-mediated transformation, which limits the effective use of genome editing technology. In this study, we describe the "optimal infiltration intensity" strategy to establish an efficient genetic transformation system for melon and squash. We harnessed the power of this method to target homologs of the ERECTA family of receptor kinase genes and created alleles resulting in a compact plant architecture with shorter internodes in melon, squash and cucumber. The optimized transformation method presented here allows stable CRISPR/Cas9-mediated mutagenesis and will lay a solid foundation for functional gene manipulation in cucurbit crops.

Agrobacterium-mediated gene transfer in plants and biosafety considerations

Agrobacterium, the natures' genetic engineer, has been used as a vector to create transgenic plants. Agrobacterium-mediated gene transfer in plants is a highly efficient transformation process which is governed by various factors including genotype of the host plant, explant, vector, plasmid, bacterial strain, composition of culture medium, tissue damage, and temperature of co-cultivation. Agrobacterium has been successfully used to transform various economically and horticulturally important monocot and dicot species by standard tissue culture and in planta transformation techniques like floral or seedling infilteration, apical meristem transformation, and the pistil drip methods. Monocots have been comparatively difficult to transform by Agrobacterium. However, successful transformations have been reported in the last few years based on the adjustment of the parameters that govern the responses of monocots to Agrobacterium. A novel Agrobacterium transferred DNA-derived nanocomplex method has been developed which will be highly valuable for plant biology and biotechnology. Agrobacterium-mediated genetic transformation is known to be the preferred method of creating transgenic plants from a commercial and biosafety perspective. Agrobacterium-mediated gene transfer predominantly results in the integration of foreign genes at a single locus in the host plant, without associated vector backbone and is also known to produce marker free plants, which are the prerequisites for commercialization of transgenic crops. Research in Agrobacterium-mediated transformation can provide new and novel insights into the understanding of the regulatory process controlling molecular, cellular, biochemical, physiological, and developmental processes occurring during Agrobacterium-mediated transformation and also into a wide range of aspects on biological safety of transgenic crops to improve crop production to meet the demands of ever-growing world's population.