Abstract
BackgroundBesides gene duplication and de novo gene generation, horizontal gene transfer (HGT) is another important way of acquiring new genes. HGT may endow the recipients with novel phenotypic traits that are important for species evolution and adaption to new ecological niches. Parasitic systems expectedly allow the occurrence of HGT at relatively high frequencies due to their long-term physical contact. In plants, a number of HGT events have been reported between the organelles of parasites and the hosts, but HGT between host and parasite nuclear genomes has rarely been found.ResultsA thorough transcriptome screening revealed that a strictosidine synthase-like (SSL) gene in the root parasitic plant Orobanche aegyptiaca and the shoot parasitic plant Cuscuta australis showed much higher sequence similarities with those in Brassicaceae than with those in their close relatives, suggesting independent gene horizontal transfer events from Brassicaceae to these parasites. These findings were strongly supported by phylogenetic analysis and their identical unique amino acid residues and deletions. Intriguingly, the nucleus-located SSL genes in Brassicaceae belonged to a new member of SSL gene family, which were originated from gene duplication. The presence of introns indicated that the transfer occurred directly by DNA integration in both parasites. Furthermore, positive selection was detected in the foreign SSL gene in O. aegyptiaca but not in C. australis. The expression of the foreign SSL genes in these two parasitic plants was detected in multiple development stages and tissues, and the foreign SSL gene was induced after wounding treatment in C. australis stems. These data imply that the foreign genes may still retain certain functions in the recipient species.ConclusionsOur study strongly supports that parasitic plants can gain novel nuclear genes from distantly related host species by HGT and the foreign genes may execute certain functions in the new hosts.
Highlights
Besides gene duplication and de novo gene generation, horizontal gene transfer (HGT) is another important way of acquiring new genes
A large set of transcriptome data was released (Parasitic Plant Genome Project; [40]). Taking advantage of these published databases, we downloaded the assembled transcriptomes of O. aegyptiaca and screened for foreign genes
A 691-bp transcript fragment showed 88 and 89% identity at the nucleotide and amino acid level, respectively, to a strictosidine synthase-like (SSL) gene in Arabidopsis thaliana (AT2G41300), while it was highly divergent from the homologs in Orobanche relative Mimulus guttatus (49% identity at the amino acid level and no significant similarities at the nucleotide level)
Summary
Besides gene duplication and de novo gene generation, horizontal gene transfer (HGT) is another important way of acquiring new genes. HGT may endow the recipients with novel phenotypic traits that are important for species evolution and adaption to new ecological niches. Retroposition, exon shuffling, trans-splicing, and de novo gene evolution, horizontal gene transfer (HGT) represents another critical source of gaining novel genes by directly introducing new genes to distantly related recipient species [1]. The separation of germ line cells from the soma expectedly leads to low HGT frequencies, genes of prokaryotic, fungal or plant origins have been discovered in diverse animals including bdelloid rotifer [8,9], tunicates [10], jelly fishes [11], starlet sea anemones [12], nematodes [13], aphids [14,15] and other insects [16,17]. Acquiring two carotenoid biosynthetic genes from fungi endowed the pea aphids with red body color, based on which the variation between green and red aphids is further driven by the predators and parasites [18]
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