Transgenic tomato plants (Solanum lycopersicum L.): direct methods of gene transfer and factors affecting transformation efficiency (review)

Tomato ( Solanum lycopersicum L.) is the most important food crop which is also widely used as a model plant in molecular genetic investigations of vegetative development and reproductive biology, plant resistance to abiotic and biotic stresses, plant-microbe association and symbiosis, etc., that have both basic and applied value. The production of transgenic tomato plants expressing foreign heterologous genes, as well as with induced silencing or knockout of their own genes, is an important part of modern plant physiology. There are two radically different approaches to introducing foreign DNA into the tomato genome. The first method is based on the natural mechanism of infection with plant-associated bacterial pathogen Agrobacterium sp. ( A. tumefaciens . or A. rhizogenes ), followed by T-DNA transfer and insertion into the plant genome ( Agrobacterim -mediated transformation). The second approach is based on the direct introducing of foreign DNA into the plant cells through the plasma membrane by chemical (Ca2+, polyethylene glycol, PEG) or physical exposure (electrical impulse or excessive pressure) (direct methods of tomato genetic transformation). Transgenic tomato plants can be produced both by the classical tissue culture-based transformation procedure and in planta transformation. This review article discusses classical direct methods for introducing foreign DNA into the tomato genome (chemical-mediated transfection, protoplast electroporation, microinjection, biolistic transformation), and in planta transformation methods (pollen-tube pathway, electroporation of mature seed embryo). The review considers features of producing tomato plants both with transient transgene expression and stably inherited insertion into the nuclear or plastid genomes are considered. In addition, the factors affecting the efficiency of transformation are analyzed in detail. A separate section is devoted to the direct tomato genetic transformation methods for delivering various genome editing tools (ZFNs, TALEN, CRISPR/Cas, base editing, prime editing) that have become widespread in the past five years.