Abstract
Hybridization between species is being recognized as a major force in the rapid adaptive evolution of fungal plant pathogens. The first stages of interspecific hybridization necessarily involve nuclear-mitochondrial chimeras. In their 2001 publication, Olson and Stenlid reported that mitochondria control the virulence of first generation hybrids between the North American fungal pathogen Heterobasidion irregulare and its congeneric H. occidentale. By assessing saprobic ability and gene expression of H. irregulare × H. annosum sensu stricto hybrids and of their parental genotypes, we demonstrate that mitochondria also influence saprobic growth of hybrids. Moreover, gene expression data suggest that fungal fitness is modulated by an intimate interplay between nuclear genes and mitochondrial type, and is dependent on the specific mitonuclear combination.
Highlights
Fungal hybridization is a process recently acknowledged to occur in nature more frequently than originally thought[1,2,3]
Fitness reduction in hybrids is being recognized as the consequence of incompatibility between mitochondrial and nuclear alleles, plausibly according to the classical biological model of evolution of genetic incompatibility known as the Bateson-Dobzhansky-Muller incompatibility (BDMI) model[7]
Olson and Stenlid[14] generated interspecific F1 heterokaryotic hybrids between the North American pine pathogen Heterobasidion irregulare and the North American non-pine pathogen H. occidentale and performed inoculation studies on pine germlings to show that hybrids with the H. irregulare mitochondria were more virulent than hybrids with the H. occidentale mitochondria
Summary
Hybridization between species is being recognized as a major force in the rapid adaptive evolution of fungal plant pathogens. The first stages of interspecific hybridization necessarily involve nuclear-mitochondrial chimeras In their 2001 publication, Olson and Stenlid reported that mitochondria control the virulence of first generation hybrids between the North American fungal pathogen Heterobasidion irregulare and its congeneric H. occidentale. Its dominance in Central Italy is associated not with higher pathogenicity on the main Italian host, Pinus pinea, but rather with its higher saprobic and sporulation potential, i.e. its greater ability to grow on wood substrates and to produce fruit bodies[19,20] These two traits ensure high establishment rates in forest stands because several Heterobasidion annosum sensu lato (s.l.) species become established through the infection of stumps by airborne spores, followed by saprobic colonization of infected stumps and stumps’ roots by vegetative mycelium[16]. This observation prompted us to confirm that fitness of admixed genotypes may be correlated with the mitochondrial genome
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