Intercollege Graduate Program in Plant Biology, Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, USA.
Department of Biology, The Pennsylvania State University, University Park, PA, USA.
Nat Plants. 2019 Sep;5(9):991-1001. doi: 10.1038/s41477-019-0458-0. Epub 2019 Jul 22.
Horizontal gene transfer (HGT), the movement and genomic integration of DNA across species boundaries, is commonly associated with bacteria and other microorganisms, but functional HGT (fHGT) is increasingly being recognized in heterotrophic parasitic plants that obtain their nutrients and water from their host plants through direct haustorial feeding. Here, in the holoparasitic stem parasite Cuscuta, we identify 108 transcribed and probably functional HGT events in Cuscuta campestris and related species, plus 42 additional regions with host-derived transposon, pseudogene and non-coding sequences. Surprisingly, 18 Cuscuta fHGTs were acquired from the same gene families by independent HGT events in Orobanchaceae parasites, and the majority are highly expressed in the haustorial feeding structures in both lineages. Convergent retention and expression of HGT sequences suggests an adaptive role for specific additional genes in parasite biology. Between 16 and 20 of the transcribed HGT events are inferred as ancestral in Cuscuta based on transcriptome sequences from species across the phylogenetic range of the genus, implicating fHGT in the successful radiation of Cuscuta parasites. Genome sequencing of C. campestris supports transfer of genomic DNA-rather than retroprocessed RNA-as the mechanism of fHGT. Many of the C. campestris genes horizontally acquired are also frequent sources of 24-nucleotide small RNAs that are typically associated with RNA-directed DNA methylation. One HGT encoding a leucine-rich repeat protein kinase overlaps with a microRNA that has been shown to regulate host gene expression, suggesting that HGT-derived parasite small RNAs may function in the parasite-host interaction. This study enriches our understanding of HGT by describing a parasite-host system with unprecedented gene exchange that points to convergent evolution of HGT events and the functional importance of horizontally transferred coding and non-coding sequences.
水平基因转移（HGT）是指 DNA 在物种间的移动和基因组整合，通常与细菌和其他微生物有关，但在从宿主植物中直接通过吸器取食来获取营养和水分的异养寄生植物中，越来越多的功能 HGT（fHGT）正在被识别。在这里，在全寄生茎寄生植物菟丝子中，我们在菟丝子属及其相关物种中鉴定出 108 个转录和可能具有功能的 HGT 事件，外加 42 个具有宿主衍生转座子、假基因和非编码序列的附加区域。令人惊讶的是，18 个菟丝子 fHGT 是由 Orobanchaceae 寄生虫中的独立 HGT 事件从相同的基因家族获得的，并且大多数在两个谱系的吸器取食结构中高度表达。HGT 序列的趋同保留和表达表明，特定的附加基因在寄生虫生物学中具有适应性作用。在基于属的系统发育范围内的物种的转录组序列中，推断出 16 到 20 个转录 HGT 事件是菟丝子的祖先，这表明 fHGT 在菟丝子寄生虫的成功辐射中发挥了作用。对菟丝子 campestris 的基因组测序支持 fHGT 的机制是基因组 DNA 的转移，而不是 retroprocessed RNA。许多水平获得的菟丝子基因也是 24 核苷酸小 RNA 的频繁来源，这些小 RNA 通常与 RNA 指导的 DNA 甲基化有关。一个编码富含亮氨酸重复蛋白激酶的 HGT 与一个 microRNA 重叠，该 microRNA 已被证明可以调节宿主基因表达，这表明 HGT 衍生的寄生虫小 RNA 可能在寄生虫-宿主相互作用中发挥作用。本研究通过描述一个具有前所未有的基因交换的寄生虫-宿主系统，丰富了我们对 HGT 的理解，这表明 HGT 事件的趋同进化和水平转移编码和非编码序列的功能重要性。
