Maize Genomics and Genetics 2024, Vol.15, No.3, 123-135 http://cropscipublisher.com/index.php/mgg 125 and "copy-and-paste." The "cut-and-paste" mechanism involves DNA transposons, which excise themselves from one genomic location and integrate into another. This process is facilitated by the enzyme transposase, which recognizes specific sequences at the ends of the transposon, cuts the DNA, and inserts the transposon into a new site (Fedoroff, 2012; Bennetzen and Wang, 2014; Romano and Fanti, 2022). Figure 1 Model for the origin ofallele SP-97 (Adopted from Sharma and Peterson, 2022) Image caption: (A) Ancestral allele, which has a structure similat to pl-wwB54-C1; The diagram shows sister chromatids and the Cl downstream of the penhancer at site a/b; (B) RET: Ac and fAc pair move from one chromatid and insert into the e/target site in the sister chromatid, causing duplication and reciprocal deletion in the sistetchromatids; (C) RET: The Ac/fAc pair on the other chromatid underwent an inversion towards p2 inserting at target site x/; (D) The lower chromatid is SP-97, which contains four copies of the p/enhancer, an inversion, a Cl, and a duplication (Adopted from Sharma and Peterson, 2022) The "copy-and-paste" mechanism is characteristic of retrotransposons, which move via an RNA intermediate. Retrotransposons are transcribed into RNA, which is then reverse-transcribed into DNA by the enzyme reverse transcriptase. The newly synthesized DNA is then integrated into a new genomic location. This mechanism not only increases the number of TEs within the genome but also contributes to genome expansion (Fedoroff, 2012; Bennetzen and Wang, 2014; Klein and O’Neill, 2018). 3.2 Enzymatic processes involved The movement of TEs within the genome is facilitated by specific enzymes, primarily transposases and reverse transcriptases. Transposases are crucial for the "cut-and-paste" mechanism of DNA transposons. These enzymes recognize terminal inverted repeats (TIRs) at the ends of the transposon, excise the transposon from its original location, and integrate it into a new site. This process is highly specific and requires precise recognition of the TIRs (Fedoroff, 2012; Bennetzen and Wang, 2014; Romano and Fanti, 2022). Reverse transcriptases are essential for the "copy-and-paste" mechanism of retrotransposons. These enzymes transcribe the RNA intermediate back into DNA, which is then integrated into the genome. The integration process is often facilitated by integrase, another enzyme that helps insert the newly synthesized DNA into the host genome (Fedoroff, 2012). The activity of these enzymes is tightly regulated to prevent uncontrolled transposition, which can lead to genomic instability (Bennetzen and Wang, 2014; Klein and O’Neill, 2018). 3.3 Regulatory mechanisms controlling TE activity The activity of TEs is tightly regulated by the host genome to prevent potential deleterious effects such as gene disruption, chromosomal rearrangements, and genome instability. One of the primary regulatory mechanisms is epigenetic modification, including DNA methylation and histone modification. These modifications can silence TEs by altering the chromatin structure, making it less accessible for transcription and transposition (Friedli and Trono, 2015; Vicient and Casacuberta, 2017; Schrader and Schmitz, 2018).
RkJQdWJsaXNoZXIy MjQ4ODYzNQ==