Table 2.

Different approaches to control MG expression levels to overcome negative pleiotropic effects

Approach	Method	Plant species	MG used	Outcome	Reference
Inducible expression	Dexamethasone-inducible system (GR fusion)	Capscium annum	BBM	Efficient regeneration of large numbers of fertile transgenic plants	Heidmann et al. (2011)
		Arabidopis thaliana	BBM	Regeneration of fertile plants during extended cultivation in tissue culture	Lutz et al. (2015)
		Theobroma cacao	LEC2	Regeneration of secondary transgenics from the leaf-derived secondary embryos	Shires et al. (2017)
	Estradiol-inducible system (OLexA promoter)	Arabidopis thaliana	MYB115	Vegetative to embryonic transition	Wang et al. (2009)
		Brassica rapa var. rapa	WUS	Fertile transgenic plants without developmental defects	Liu et al. (2022)
Excision-based	Desiccation-inducible CRE/LOXP	Zea mays	WUS2+BBM	Excision of the morphogenic genes to produce healthy, fertile transgenic plants	Lowe et al. (2016)
	Heat shock-inducible FLP/FRT	Populus tomentosa	BBM	Transgenic plants with phenotypic alterations but fertile	Deng et al. (2009)
Tissue-specific promoters	AXIG1 promoter PLTP promoter	Zea mays	BBM+WUS2	Robust and fertile transgenic plants even without excision of MG	Lowe et al. (2018)
GRF–GIF chimeras	–	Triticum aestivum Oryza sativa Citrus Cannabis sativa	GRF4–GIF1 GRF3–GIF1	Fertile transgenic plants without developmental defects	Debernardi et al. (2020); Zhang et al. (2021)
Agrobacterium-mediated delivery methods	Two Agrobacterium strains with each harbouring a distinct T-DNA	Sorghum bicolor	WUS+CRC	Somatic embryo formation and regeneration of stable transgenic plants with only the selectable marker	Hoerster et al. (2020)
T-DNA border read-through	Positioning MG cassettes outside T-DNA left border	Zea mays	WUS2 WUS2+BBM	Non-excision method for creating a high-quality transgenic event	Gordon-Kamm et al. (2019)