New opportunities for using WUS/BBM and GRF-GIF genes to enhance genetic transformation of ornamental plants

Broad application of plant transformation remains challenging because the efficiency of plant regeneration and regeneration-based transformation in many plant species is extremely low. Many species and genotypes are not responsive to traditional hormone-based regeneration systems. This regeneration recalcitrance hampers the application of many technologies such as micropropagation, transgenic breeding, and gene editing in various plant species, including ornamental flowers, shrubs, and trees. Various developmental genes have long been studied for their ability to improve plant meristematic induction and regeneration. Lately, it was demonstrated that the combined and refined expression of morphogenic regulator genes WUSCHEL and BABY BOOM could alleviate their pleiotropic effects and permit transformation in recalcitrant monocots. Moreover, ectopic expression of plant growth-regulating factors (GRFs) alone or in combination with GRF-interacting factors (GIFs) improved the regeneration and transformation of dicot and monocot species. Fine-tuning the expression of these genes provides new opportunities to improve transformation efficiencies and facilitate the application of new breeding technologies in ornamental plants.