Heterobasidion annosum s.l. Biology, genomics, and pathogenicity factors

In boreal and north temperate forests, about 10%-15% of conifer trees (spruce, pine) cut are rotted and commercially less valuable, largely caused by a single pathogen Heterobasidion annosum s.l. The economic effects of Heterobasidion infection approximate to 1 billion euros in losses yearly in Europe. Despite extensive efforts dedicated to unravel the genetic components involved in the pathogenicity and lifestyles of Heterobasidion pathogens, the molecular mechanisms have not been thoroughly understood. Our understanding and perception of Heterobasidion pathogenesis have recently been facilitated due to novel technological advances using “Omics” technology. The availability of the genome and transcriptome of Heterobasidion has led to the discovery of large groups of small secreted proteins (SSPs) or effector-like proteins. Elucidating the functional role of the individual effectors is, however, a very challenging task. Despite the perceived progress, there are still intractable challenges working with Heterobasidion-conifer pathosystem; the long timescale of the disease, lack of mutant lines, large genome size of the host, no avirulent isolates of the pathogen, and inefficient DNA transformation system are some of the obstacles. In spite of the challenges, there have been novel prospects for advances. Novel biotechnology methods are now available and can be deployed to answer many of the fundamental biological questions in this pathosystem.