Ambrose Karen V, Koppenhöfer Albrecht M, Belanger Faith C
Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ 08901.
Department of Entomology, Rutgers University, New Brunswick, NJ 08901.
Sci Rep. 2014 Jul 3;4:5562. doi: 10.1038/srep05562.
Horizontal gene transfer is recognized as an important factor in genome evolution, particularly when the newly acquired gene confers a new capability to the recipient species. We identified a gene similar to the makes caterpillars floppy (mcf1 and mcf2) insect toxin genes in Photorhabdus, bacterial symbionts of nematodes, in the genomes of the Epichloë fungi, which are intercellular symbionts of grasses. Infection by Epichloë spp. often confers insect resistance to the grass hosts, largely due to the production of fungal alkaloids. A mcf-like gene is present in all of the Epichloë genome sequences currently available but in no other fungal genomes. This suggests the Epichloë genes were derived from a single lineage-specific HGT event. Molecular dating was used to estimate the time of the HGT event at between 7.2 and 58.8 million years ago. The mcf-like coding sequence from Epichloë typhina subsp. poae was cloned and expressed in Escherichia coli. E. coli cells expressing the Mcf protein were toxic to black cutworms (Agrotis ipsilon), whereas E. coli cells containing the vector only were non-toxic. These results suggest that the Epichloë mcf-like genes may be a component, in addition to the fungal alkaloids, of the insect resistance observed in Epichloë-infected grasses.
水平基因转移被认为是基因组进化中的一个重要因素，尤其是当新获得的基因赋予受体物种新能力时。我们在Epichloë真菌（禾本科植物的细胞内共生菌）的基因组中，发现了一种与线虫的细菌共生菌发光杆菌属（Photorhabdus）中使毛虫变软（mcf1和mcf2）的昆虫毒素基因相似的基因。Epichloë spp.的感染通常会使禾本科宿主产生抗虫性，这主要是由于真菌生物碱的产生。目前所有可用的Epichloë基因组序列中都存在一个类似mcf的基因，但在其他真菌基因组中则没有。这表明Epichloë基因源自单一的谱系特异性水平基因转移事件。分子年代测定法用于估计水平基因转移事件发生的时间在720万至5880万年前之间。克隆了来自Epichloë typhina subsp. poae的类似mcf的编码序列，并在大肠杆菌中进行表达。表达Mcf蛋白的大肠杆菌细胞对小地老虎（Agrotis ipsilon）有毒，而仅含有载体的大肠杆菌细胞则无毒。这些结果表明，除了真菌生物碱外，Epichloë类似mcf的基因可能是Epichloë感染的禾本科植物中观察到的抗虫性的一个组成部分。
