Galindo-González Leonardo, Mhiri Corinne, Deyholos Michael K, Grandbastien Marie-Angèle
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, RD10, 78026 Versailles Cedex, France.
Gene. 2017 Aug 30;626:14-25. doi: 10.1016/j.gene.2017.04.051. Epub 2017 May 2.
LTR retrotransposons are the most abundant group of transposable elements (TEs) in plants. These elements can fall inside or close to genes, and therefore influence their expression and evolution. This review aims to examine how LTR retrotransposons, especially Ty1-copia elements, mediate gene regulation and evolution. Various stimuli, including polyploidization and biotic and abiotic elicitors, result in the transcription and movement of these retrotransposons, and can facilitate adaptation. The presence of cis-regulatory motifs in the LTRs are central to their stress-mediated responses and are shared with host stress-responsive genes, showing a complex evolutionary history in which TEs provide new regulatory units to genes. The presence of retrotransposon remnants in genes that are necessary for normal gene function, demonstrates the importance of exaptation and co-option, and is also a consequence of the abundance of these elements in plant genomes. Furthermore, insertions of LTR retrotransposons in and around genes provide potential for alternative splicing, epigenetic control, transduction, duplication and recombination. These characteristics can become an active part of the evolution of gene families as in the case of resistance genes (R-genes). The character of TEs as exclusively selfish is now being re-evaluated. Since genome-wide reprogramming via TEs is a long evolutionary process, the changes we can examine are case-specific and their fitness advantage may not be evident until TE-derived motifs and domains have been completely co-opted and fixed. Nevertheless, the presence of LTR retrotransposons inside genes and as part of gene promoter regions is consistent with their roles as engines of plant genome evolution.
长末端重复序列(LTR)逆转录转座子是植物中最丰富的一类转座元件(TEs)。这些元件可插入基因内部或靠近基因的位置,从而影响基因的表达和进化。本综述旨在探讨LTR逆转录转座子,尤其是Ty1-copia元件,如何介导基因调控和进化。包括多倍体化以及生物和非生物诱导子在内的各种刺激,会导致这些逆转录转座子的转录和移动,并有助于植物适应环境。LTR中顺式调控基序的存在是其应激介导反应的核心,并且与宿主应激反应基因共有,这显示出一个复杂的进化历程,其中转座元件为基因提供了新的调控单元。在正常基因功能所必需的基因中存在逆转录转座子残余,证明了功能改变和功能借用的重要性,这也是这些元件在植物基因组中大量存在的结果。此外,LTR逆转录转座子在基因内部及其周围的插入为可变剪接、表观遗传控制、转导、基因复制和重组提供了可能性。这些特性可以成为基因家族进化的一个活跃部分,例如在抗性基因(R基因)的情况中。现在人们正在重新评估转座元件完全自私的特性。由于通过转座元件进行全基因组重编程是一个漫长的进化过程,我们能够研究的变化是特定于具体情况的,并且在转座元件衍生的基序和结构域被完全借用并固定之前,其适应性优势可能并不明显。然而,基因内部以及作为基因启动子区域一部分的LTR逆转录转座子的存在,与它们作为植物基因组进化引擎的作用是一致的。