Maize Genomics and Genetics 2024, Vol.15, No.3, 147-159 http://cropscipublisher.com/index.php/mgg 149 DNA transposons, also known as Class II transposons, move directly as DNA through a "cut-and-paste" mechanism. This involves the excision of the transposon from one genomic location and its integration into another, facilitated by the enzyme transposase (Johnson and Reznikoff, 1983; Feschotte and Pritham, 2007; Hickman and Dyda, 2016). Retrotransposons, or Class I transposons, move via an RNA intermediate. This process involves transcription of the transposon into RNA, reverse transcription into DNA, and integration of the new DNA copy into the genome. Retrotransposons are further divided into long terminal repeat (LTR) and non-LTR retrotransposons (Hancks and Kazazian, 2012). In Zea mays (maize), both DNA transposons and retrotransposons are prevalent and play significant roles in genome evolution and diversity. The maize genome is particularly rich in transposable elements, which constitute a substantial portion of its genetic material. The classification of these elements is crucial for understanding their impact on the genetic architecture of maize, as different types of transposons have distinct mechanisms of transposition and genomic effects (Feschotte and Pritham, 2007; Huang et al., 2012; Burns, 2020). 3.2 Key transposon families Among the various transposon families in Zea, the most notable include the Activator (Ac)/Dissociation (Ds) system, the Mutator (Mu) family, and the Helitron family. The Ac/Ds system is a well-studied DNA transposon family in maize. The Ac element encodes a transposase that facilitates its own movement as well as the movement of non-autonomous Ds elements, which lack functional transposase genes (Johnson and Reznikoff, 1983; Feschotte and Pritham, 2007). This system has been instrumental in studying gene function and regulation in maize. The Mutator family is another significant group of DNA transposons in maize. These elements are highly mutagenic and have been extensively used in genetic studies to induce mutations and identify gene functions. The Mu elements are characterized by their high transposition activity and ability to generate a wide range of genetic variations (Feschotte and Pritham, 2007; Huang et al., 2012). Helitrons represent a unique family of rolling-circle transposons that have been identified in maize. Unlike other DNA transposons, Helitrons replicate through a rolling-circle mechanism, which involves the formation of a single-stranded DNA intermediate. This family of transposons is known for capturing and shuffling gene fragments, thereby contributing to genome plasticity and evolution (Feschotte and Pritham, 2007; Hickman and Dyda, 2012). 3.3 Mechanisms of transposition The mechanisms of transposition vary among different types of transposons, but they generally involve a series of well-coordinated steps. For DNA transposons, the process typically begins with the recognition of specific DNA sequences at the ends of the transposon by the transposase enzyme. The transposase then catalyzes the excision of the transposon from its original location and its integration into a new genomic site. This "cut-and-paste" mechanism is characteristic of many DNA transposons, including the Ac/Ds and Mu elements in maize (Johnson and Reznikoff, 1983; Feschotte and Pritham, 2007; Hickman and Dyda, 2016). Retrotransposons, on the other hand, utilize a "copy-and-paste" mechanism. The transposition process starts with the transcription of the retrotransposon into RNA, followed by reverse transcription into DNA by the enzyme reverse transcriptase. The newly synthesized DNA copy is then integrated into a new genomic location. This mechanism is typical of LTR and non-LTR retrotransposons, which are abundant in the maize genome (Fedoroff, 2012; Hancks and Kazazian, 2012). Helitrons employ a distinct rolling-circle replication mechanism. The process involves the formation of a single-stranded DNA intermediate, which is then used as a template for the synthesis of a new double-stranded DNA copy. This new copy is subsequently integrated into the genome. The unique mechanism of Helitrons allows them to capture and mobilize gene fragments, contributing to genetic diversity and innovation in maize (Feschotte and Pritham, 2007; Hancks and Kazazian, 2012). The diverse mechanisms of transposition employed by different
RkJQdWJsaXNoZXIy MjQ4ODYzNQ==