Power of the palindrome in evolution
Transposons can be actively deleterious to a genome and our bodies have evolved many protective mechanisms to curb TE activity. These silencing systems often revolve around small RNA molecules that guide methylation in the area of a TE. A resulting dense chromatin mass around the TE physically restricts transcription and is known as gene capturing. Escape from silencing for TEs is a possible strategy given how prolific they are in genomes. The EU-funded ADAPTED (The role of adaptive evolution in the success of transposable elements) project has investigated how this comes about. The researchers focused on Sirevirus, an ancient TE genus that makes up almost 20 % of the maize genome. ADAPTED retrieved the original maize Sirevirus population and produced almost 6 500 full-length Sireviruses that are divided into 5 families. The study then focused on the rates of adaptive evolution in relation to successful life history and adaptation against host defences. Examination of silencing marks provided strong evidence of cis-regulatory TE regions as targets of host defences. Sireviruses contain many palindromes in a domain that controls part of their life cycle. Sequence evolution of the palindromes may help TEs to escape silencing and hosts may use the palindromes in old Sireviruses for rapid transformation to produce small RNAs to new highly dangerous relatives. Papers from the research of ADAPTED have appeared in Nature, Science, Brmc Genomics and Plant Journal. ADAPTED has constructed a firm knowledge platform involving population genetics, molecular evolution using statistical analysis and mathematical modelling. Application of the results could be wide-ranging given the sheer numbers of TEs in all eukaryotes.
Keywords
Palindrome, evolution, transposable elements, Sirevirus, maize
