Agrobacterium-mediated transformation: state of the art and future prospect

Agroinfiltration Mediated Scalable Transient Gene Expression in Genome Edited Crop Plants

Agrobacterium-mediated transformation is one of the most commonly used genetic transformation method that involves transfer of foreign genes into target plants. Agroinfiltration, an Agrobacterium-based transient approach and the breakthrough discovery of CRISPR/Cas9 holds trending stature to perform targeted and efficient genome editing (GE). The predominant feature of agroinfiltration is the abolishment of Transfer-DNA (T-DNA) integration event to ensure fewer biosafety and regulatory issues besides showcasing the capability to perform transcription and translation efficiently, hence providing a large picture through pilot-scale experiment via transient approach. The direct delivery of recombinant agrobacteria through this approach carrying CRISPR/Cas cassette to knockout the expression of the target gene in the intercellular tissue spaces by physical or vacuum infiltration can simplify the targeted site modification. This review aims to provide information on Agrobacterium-mediated transformation and implementation of agroinfiltration with GE to widen the horizon of targeted genome editing before a stable genome editing approach. This will ease the screening of numerous functions of genes in different plant species with wider applicability in future.

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.

Transformation of cambial tissue in vivo provides an efficient means for induced somatic sector analysis and gene testing in stems of woody plant species

Large-scale functional analysis of genes and transgenes suspected to be involved in wood development in trees is hindered by long generation times, low transformation and regeneration efficiencies and difficulties with phenotypic assessment of traits, especially those that appear late in a tree's development. To avoid such obstacles many researchers have turned to model plants such as Arabidopsis thaliana (L.) Heynh., Zinnia elegans Jacq. and Nicotiana ssp., or have focused their attention on in vitro wood formation systems or in vivo approaches targeting primary meristems for transformation. Complementing such efforts, we report the use of Agrobacterium to introduce transgenes directly into cambial cells of glasshouse-grown trees in order to create transgenic somatic tissue sectors. These sectors are suitable for phenotypic evaluation and analysis of target gene function. In our experiments the wood formation zone containing the cambium of Eucalyptus, Populus and Pinus species of varying age was inoculated with Agrobacterium containing a CaMV 35S::GUS construct. Following an initial wound response, frequent and stable transformation was observed in the form of distinct GUS-staining patterns (sectors) in newly formed secondary tissues. Sector size and extent depended on the cell type transformed, the species and the length of time treated plants were allowed to grow (more than two years in some cases). Induced somatic sector analysis (ISSA) can now be efficiently used to study cell fate and gene function during secondary growth in stems of forest tree species.