GENETICALLY MODIFIED CORN IN BRAZIL: HISTORICAL, RESULTS AND PERSPECTIVES

The objective of this work was to review the history of genetically modified (GM) corn in Brazil, and the results obtained since its introduction, as well as the perspectives for new technologies. GM corn was planted for the first time in Brazil in 2008 and, a few years later, it reached more than 80% of the planted area. Currently, the GM corn area in Brazil is close to 90%. The traits introduced in corn are related to herbicide tolerance and insect resistance, and the benefits for farmers and the environment in these 12 years were enormous. GM events also impacted plant breeding, and breeding methods needed to be adapted to include the introduction of GM events into germplasm. New emerging technologies, such as gene editing and synthetic biology, may have a new impact on corn improvement, creating new traits, many of them non-transgenic. These new technologies have the potential to improve traits associated with plant yield and tolerance to abiotic stresses.

Law. To date, CTNBio has been issued commercial clearance for corn, soybean, cotton, bean, eucalyptus, and sugarcane traits. Corn traits that received approval for cultivation are most composed by herbicide tolerance, insect resistance, and combinations of these traits. season, 52% of cultivars were exclusively for grains, 45% for silage, and 3% special use (Pereira Filho and Borghi, 2020). The main technologies and combinations are described in Table 1 and Table 2.

Insect Resistance Traits
Insect control in corn fields is probably one of the most challenging topics in pest control. Insecticide proteins were first isolated from  and Cry1F (Wang et al., 2020). ABC transporters are membrane-associate ATP-dependent proteins involved in transporting several substrates including lipids, peptides, amino acids, sugars, and xenobiotics (Wu et al., 2019). Mutational disruption of ABCC2 in FAW confers resistance to Cry1F and Cry1A.105 (Flagel et al., 2018) but no resistance was observed for ABCC3 mutation . The sequencing of ABCC2 gene from two Cry1F field resistant populations in Brazil identified a GY deletion (positions 788-789) and a P799K/R substitution at the extracellular loop 4 (Boaventura et al., 2020). In addition to loop4, ABCC2 loop 2 is also seems responsible for Cry1F insecticidal activity , probably serving as the toxin binding site.
Besides the desirable high-dose levels Bt proteins, both present in the same cultivar (Pittendrigh et al., 2013). The opposite would be the positive cross-resistance, which is found on insect populations that are resistant to one Bt protein that also exhibit resistance to other Bt proteins, usually by toxins that share similarities on the protein structure and possibly the same receptor on target pests (Carrière et al., 2015). constitutively produces (E)-β-caryophyllene, a terpenoid frequently linked with resistance and acts by repelling FAW from feeding (Smith et al., 2012). The induction of defensive genes also plays important roles for controlling insect damage. Ribosome-inactivating protein 2 (RIP2) expression is largely induced in corn by insect larvae feeding but not by mechanical wounding. RIP2 expression is also influenced by several phytohormones, including methyl jasmonate, ethylene, and abscisic acid and its presence in corn leaves can retard caterpillar growth (Chuang et al., 2014). These natural mechanisms found on corn reiterates the importance of identification and combination of different native resistance mechanisms into corn germplasm that will be the basis for the introgression of Bt traits. This strategy seems to be also a viable option to increase Bt product efficacy and contribute to avoid resistance Refuge strategy consists of planting a structured area of non-Bt crops, and has been shown to be valuable for both singles and pyramided Bt products (Carrière et al., 2020). These areas are hosts to insects that are susceptible to Bt toxins, and therefore contribute to maintaining susceptible allele   Introducing part of the traits in one parent an part in other parent, the population size can be reduced in 50% in the case of four inserts, and the reduction in population size can reach 67.5% in the case of five insertions (Figure 4).
On the other hand, as introducing traits in two parents means having two parents in the backcross program, and the activities related to completion and test of converted inbreed lines and seed increase of new parent version is twice as the activities when just one parent is converted.

The introduction of new GM traits in
corn breeding also potentially is associated with a reduction in the speed of genetic gain. When a new GM trait is introduced in a corn breeding program, it is expected the current best testers will be converted first. It means the same testers will be used for some more years. New good candidates for testers, as they have not yet been well proven, will be converted after the wellknown testers. As a result, the change in the testers, or the use of new testers, can be delayed, resulting in delaying the genetic gain associated with the new tester. The alternative to avoid this delay in genetic gain is to convert as many parents as possible, especially testers, at the same time. But it is also associated with the increase in breeding costs.

Future Prospect
Over  (Yang et al., 2017). Crops requiring less use of agrochemicals are in high demand, especially for industrial fertilizers, which production have been associated to environmental pollution and expressive manufacture costs.
Ambitious projects are currently aiming the utilization of SynBio to rebuild entire yeast genome, synthetizing and mounting each chromosome (Richardson et al., 2017). These forms of basic research help to elucidate the most fundamental principles of life chemistry, making possible the proposal of until then distant applications like producing a synthetic chloroplast genome (Piatek et al., 2018). Chloroplasts are the core of photosynthesis and also target of multiples virus in plants (Zhao et al., 2016). Corn chloroplast genome has only 140 kb in length and contains 118 genes, which makes straightforward a complete redesignation, when compared to nuclear genome (Chen et al., 2020