Intergeneric transfer of ribosomal genes between two fungi

Jiatao Xie,Youliang Peng,Tom Hsiang,Daohong Jiang,Guoqing Li,Junbin Huang,Yanping Fu,Bo Li

doi:10.1186/1471-2148-8-87

Abstract

BackgroundHorizontal gene transfer, also called lateral gene transfer, frequently occurs among prokaryotic organisms, and is considered an important force in their evolution. However, there are relatively few reports of transfer to or from fungi, with some notable exceptions in the acquisition of prokaryotic genes. Some fungal species have been found to contain sequences resembling those of bacterial genes, and with such sequences absent in other fungal species, this has been interpreted as horizontal gene transfer. Similarly, a few fungi have been found to contain genes absent in close relatives but present in more distantly related taxa, and horizontal gene transfer has been invoked as a parsimonious explanation. There is a paucity of direct experimental evidence demonstrating the occurrence of horizontal gene transfer in fungi.ResultsWe found a fungal field isolate from rice (Oryzae sativa) that contains ribosomal DNA sequences from two species of fungal rice pathogens (Thanatephorus cucumeris and Ceratobasidium oryzae-sativae). This field isolate has four types of ribosomal DNA internal transcribed spacers (ITS), namely pure ITS of C. oryzae-sativae, which was dominant in this field isolate, pure ITS of T. cucumeris, and two chimeric ITS, with ITS1 derived from C. oryzae-sativae and ITS2 from T. cucumeris, or ITS1 from T. cucumeris and ITS2 from C. oryzae-sativae. The presence of chimeric forms indicates that the intergeneric hybrid was not merely composed of nuclei from the parental species, but that nuclear fusion and crossing over had taken place.ConclusionHyphae of T. cucumeris and C. oryzae-sativae are vegetatively incompatible, and do not successfully anastomose. However, they parasitize the same host, and perhaps under the influence of host enzymes targeted to weaken pathogen cells or in dying host plant tissue, the fungal hyphae lost their integrity, and normal vegetative incompatibility mechanisms were overcome, allowing the hyphae to fuse. Based on the presence of other similarly anomalous isolates from the field, we speculate that these types of intergeneric hybridization events and occurrences of horizontal gene transfer may not be so rare in the field.

Highlights

Horizontal gene transfer, called lateral gene transfer, frequently occurs among prokaryotic organisms, and is considered an important force in their evolution
Some species have been found to contain sequences resembling those of bacterial genes, but such sequences were absent in other fungal species, and this was interpreted as Horizontal gene transfer (HGT) [5,6,7,8,9,10]
The growth rate of RCOL-1 was slower than the average for either of the two major fungal rice pathogens Thanatephorus cucumeris or Ceratobasidium oryzae-sativae

Summary

Introduction

Horizontal gene transfer, called lateral gene transfer, frequently occurs among prokaryotic organisms, and is considered an important force in their evolution. Some fungal species have been found to contain sequences resembling those of bacterial genes, and with such sequences absent in other fungal species, this has been interpreted as horizontal gene transfer. Horizontal gene transfer (HGT), called lateral gene transfer, is known to occur among prokaryotic organisms, and is considered an important force in their evolution [1], but HGT is less well known among eukaryotes [2]. Some species have been found to contain sequences resembling those of bacterial genes, but such sequences were absent in other fungal species, and this was interpreted as HGT [5,6,7,8,9,10]. A nitrate assimilation gene cluster was thought to have been transferred first from Oomycota to Dikarya (Ascomycota and Basidiomycota), and more recently from a basdiomycete to the ascomycete Trichoderma reesei, which allowed this fungus to better exploit its new niche [13]

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