回文结构在玉米Sirevirus LTRs顺式区域中在转座元件进化和宿主表观遗传反应中的作用。
A role for palindromic structures in the cis-region of maize Sirevirus LTRs in transposable element evolution and host epigenetic response.
作者信息
Bousios Alexandros, Diez Concepcion M, Takuno Shohei, Bystry Vojtech, Darzentas Nikos, Gaut Brandon S
机构信息
School of Life Sciences, University of Sussex, Brighton BN1 9RH, United Kingdom; Institute of Applied Biosciences, Centre for Research and Technology Hellas, 57001 Thessaloniki, Greece;
Department of Agronomy, University of Cordoba, 14014 Cordoba, Spain; Department of Ecology and Evolutionary Biology, UC Irvine, Irvine, California 92697, USA;
出版信息
Genome Res. 2016 Feb;26(2):226-37. doi: 10.1101/gr.193763.115. Epub 2015 Dec 2.
Transposable elements (TEs) proliferate within the genome of their host, which responds by silencing them epigenetically. Much is known about the mechanisms of silencing in plants, particularly the role of siRNAs in guiding DNA methylation. In contrast, little is known about siRNA targeting patterns along the length of TEs, yet this information may provide crucial insights into the dynamics between hosts and TEs. By focusing on 6456 carefully annotated, full-length Sirevirus LTR retrotransposons in maize, we show that their silencing associates with underlying characteristics of the TE sequence and also uncover three features of the host-TE interaction. First, siRNA mapping varies among families and among elements, but particularly along the length of elements. Within the cis-regulatory portion of the LTRs, a complex palindrome-rich region acts as a hotspot of both siRNA matching and sequence evolution. These patterns are consistent across leaf, tassel, and immature ear libraries, but particularly emphasized for floral tissues and 21- to 22-nt siRNAs. Second, this region has the ability to form hairpins, making it a potential template for the production of miRNA-like, hairpin-derived small RNAs. Third, Sireviruses are targeted by siRNAs as a decreasing function of their age, but the oldest elements remain highly targeted, partially by siRNAs that cross-map to the youngest elements. We show that the targeting of older Sireviruses reflects their conserved palindromes. Altogether, we hypothesize that the palindromes aid the silencing of active elements and influence transposition potential, siRNA targeting levels, and ultimately the fate of an element within the genome.
转座元件(TEs)在其宿主基因组中增殖,宿主通过表观遗传沉默来应对。我们对植物中的沉默机制了解很多,尤其是小干扰RNA(siRNAs)在引导DNA甲基化中的作用。相比之下,关于沿着TEs长度的siRNA靶向模式却知之甚少,然而这些信息可能为宿主与TEs之间的动态关系提供关键见解。通过聚焦于玉米中6456个经过仔细注释的全长Sirevirus LTR反转录转座子,我们表明它们的沉默与TE序列的潜在特征相关联,并且还揭示了宿主 - TE相互作用的三个特征。首先,siRNA定位在不同家族和不同元件之间存在差异,但特别是沿着元件的长度。在LTRs的顺式调控部分内,一个复杂的富含回文序列的区域既是siRNA匹配的热点,也是序列进化的热点。这些模式在叶片、雄穗和未成熟穗文库中是一致的,但在花组织和21至22个核苷酸的siRNAs中尤为突出。其次,该区域有形成发夹结构的能力,使其成为产生类似miRNA的、源自发夹结构的小RNA的潜在模板。第三,Sireviruses被siRNAs靶向的程度与其年龄成反比,但最古老的元件仍然受到高度靶向,部分是被交叉映射到最年轻元件的siRNAs靶向。我们表明,对较古老的Sireviruses的靶向反映了它们保守的回文序列。总之,我们推测回文序列有助于沉默活跃元件,并影响转座潜力、siRNA靶向水平,最终影响基因组中元件的命运。