The Homologue ofhet-cofNeurospora crassaLacks Vegetative Compatibility Function inFusarium proliferatum

Abstract

For two fungal strains to be vegetatively compatible and capable of forming a stable vegetative heterokaryon they must carry matching alleles at a series of loci variously termed het or vic genes. Cloned het/vic genes from Neurospora crassa and Podospora anserina have no obvious functional similarity and have various cellular functions. Our objective was to identify the homologue of the Neurospora het-c gene in Fusarium proliferatum and to determine if this gene has a vegetative compatibility function in this economically important and widely dispersed fungal pathogen. In F. proliferatum and five other closely related Fusarium species we found a few differences in the DNA sequence, but the changes were silent and did not alter the amino acid sequence of the resulting protein. Deleting the gene altered sexual fertility as the female parent, but it did not alter male fertility or existing vegetative compatibility interactions. Replacement of the allele-specific portion of the coding sequence with the sequence of an alternate allele in N. crassa did not result in a vegetative incompatibility response in transformed strains of F. proliferatum. Thus, the fphch gene in Fusarium appears unlikely to have the vegetative compatibility function associated with its homologue in N. crassa. These results suggest that the vegetative compatibility phenotype may result from convergent evolution. Thus, the genes involved in this process may need to be identified at the species level or at the level of a group of species and could prove to be attractive targets for the development of antifungal agents.Fungal cells can interact with each other either vegetatively or sexually. In ascomycete fungi, sexual interactions are controlled by the alleles at the mating type locus (MAT), and asexual interactions are controlled by the alleles at the vic (vegetative incompatibility) or het (heterokaryon incompatibility) loci (20). (het and vic are used to indicate genes with similar functions and reflect differences in nomenclature, not function.) Vegetative incompatibility has been studied at least superficially in a large number of fungi, but in-depth studies have been limited to Neurospora crassa (12,34,35,36), Podospora anserina (7,10,29,30), Cryphonectria parasitica (6), Aspergillus nidulans (8), and several species of Fusarium (13,17,25,26). The het/vic genes are important for the recognition process to occur, but there are genes that affect the physical ability of hyphae to fuse that act upstream of the het/vic interaction (5, 23) and other genes that are responsible for maintaining the stability of the heterokaryon that act following the het/vic interaction (23,40

Self/nonself recognition in Tuber melanosporum is not mediated by a heterokaryon incompatibility system

“…As its deletion does not lead to any detectable phenotype, no cellular functions in addition to its role in HI have been hypothesized for N. crassa het-c (Saupe 2000). However, identification of two HET-C domain proteins in T. melanosporum and the high level of conservation of the HET-C orthologues throughout the filamentous ascomycetes genomes sequenced to date support the assumption of their specific role in cellular functioning Ker enyi et al 2006). Nonself recognition at the N. crassa het-c locus is mediated by essential nonallelic interactions between the closely linked loci het-c and pin-c and an allelic interaction at het-c which increases the severity of the HI phenotype (Kaneko et al 2006).…”

“…No evidence for pin-c homologue closely linked to tmelhetC135 was detected in the T. melanosporum genome but putative genes encoding an alpha-1,3-glucan synthase and a RNA binding protein not related with HI are located w10 kb upstream and w3 kb downstream, respectively (data not shown). In addition the lack of polymorphisms at the het-c loci of P. anserina, Aspergillus nidulans, A. niger, and Fusarium proliferatum, as also found for T. melanosporum tmelhetC135, suggested that they indeed do not function as het genes in these filamentous ascomycetes during HI Davies et al 2004;Ker enyi et al 2006;Van Diepeningen et al 2008).…”

The social evolution of somatic fusion

“…First, often, kin-recognition genes are completely unrelated between species. (48,49) Second, and most importantly, in many cases, kin-recognition genes have other functions in addition to their role in restricting somatic fusion. Some of these functions could stabilize the observed polymorphisms (summarized in Table 2).…”

Gibberellins and Other Metabolites of Fusarium fujikuroi and Related Fungi

“…Sexual activity is not a valid systematic trait, because its observation may depend on the culture conditions and its absence may be caused by a single mutation. F. fujikuroi was taken back to the genus Fusarium and divided into several new species on the basis of cross fertility [33,34] and DNA sequences [35]; this process is not closed, and new species are under consideration [36].…”