Horizontal transfer of the Ophiostoma gene encoding cerato-ulmin into unrelated species of the genus Geosmithia.

Horizontal gene transfer (HGT) is a relevant evolutionary mechanism by which plant pathogens have emerged in agro-ecosystems over different time scales. In the prokaryotes HGT is generally considered a major factor for the evolution of genomes, whereas in fungi HGT is assumed to play a minor role, just to justify unusual features of genetic elements such as single genes or gene clusters. In the present work we demonstrated that strains belonging to Geosmithia pallida and G. langdonii possess and express the cu gene coding the cerato-ulmin (CU) hydrophobin. CU is produced by various Ophiostoma species (a taxon distant from the genus Geosmithia), and to give the Ophiostomas causing Dutch elm disease key advantages in parasitic fitness and virulence. We are working to understand how and why a portion of the genome of Ophiostoma novo-ulmi, including the cu gene, has been transferred in Geosmithia strains, and what advantages, in terms of fungal fitness, there are for the Geosmithias by acquiring this gene. Moreover, we are characterizing the CUs produced by the Geoesmithias and investigating how they behave towards the elms.