Three strategies of transgenic manipulation for crop improvement

Abstract

Heterologous expression of exogenous genes, overexpression of endogenous genes, and suppressed expression of undesirable genes are the three strategies of transgenic manipulation for crop improvement. Up to 2020, most (227) of the singular transgenic events (265) of crops approved for commercial release worldwide have been developed by the first strategy. Thirty-eight of them have been transformed by synthetic sequences transcribing antisense or double-stranded RNAs and three by mutated copies for suppressed expression of undesirable genes (the third strategy). By the first and the third strategies, hundreds of transgenic events and thousands of varieties with significant improvement of resistance to herbicides and pesticides, as well as nutritional quality, have been developed and approved for commercial release. Their application has significantly decreased the use of synthetic pesticides and the cost of crop production and increased the yield of crops and the benefits to farmers. However, almost all the events overexpressing endogenous genes remain at the testing stage, except one for fertility restoration and another for pyramiding herbicide tolerance. The novel functions conferred by the heterologously expressing exogenous genes under the control of constitutive promoters are usually absent in the recipient crops themselves or perform in different pathways. However, the endogenous proteins encoded by the overexpressing endogenous genes are regulated in complex networks with functionally redundant and replaceable pathways and are difficult to confer the desirable phenotypes significantly. It is concluded that heterologous expression of exogenous genes and suppressed expression by RNA interference and clustered regularly interspaced short palindromic repeats-cas (CRISPR/Cas) of undesirable genes are superior to the overexpression of endogenous genes for transgenic improvement of crops.

Breeding Cassava for End-User Needs

“…Cassava genetic transformation efforts have been used in improving traits such as CMD resistance, increase in protein content from 40 to 130% and improved starch content and quality [25]. For the development of transgenic cultivars, desirable genes are cloned, vectors are constructed, crops are transformed, and subsequently, screening and identification of transformed lines are conducted [23,26]. Through a concerted effort of several laboratories for about 25 years, transformation of cassava and the use of Agrobacterium tumefaciens or particle bombardment as gene delivery system became a reality.…”

The battle of crops against drought: Genetic dissection and improvement

“…Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated nuclease (Cas) has been utilized as a genome editing tool for crop breeding (Nadeem et al, 2019; Sami et al, 2021; Yu et al, 2022). Key regulators and interaction networks controlling drought tolerance have been identified, some of which have been accurately edited for trait improvement in germplasm resources.…”

Transgenic Improvement for Biotic Resistance of Crops

“…The second strategy is the transformation of endogenous genes from the same species or homologous genes from sexually compatible species. The third strategy is silencing the expression of undesirable endogenous or pathogenic and pest genes by RNAi) or CRISPR/Cas technology [162].…”