Ash dieback is a fungal disease (caused by Chalara fraxinea) lethal to ash trees, spreading across Europe since being first detected (in Eastern Europe) in 1992. It was found in the UK in England in March 2012 and has now also been found in Scotland, Wales and Northern Ireland. Its spread is hastened by individuals transporting young ash trees from one area to another. Ash dieback is not believed to be harmful to animal or human health. Picture shown is from BBC news website.
Molecular genetics of ash dieback disease
Investigations using the latest techniques have been carried out rapidly to understand how the fungus kills ash trees at the molecular level. The aim is to be able in the long term to find ways of stopping, or slowing the spread of, this disease, which threatens the 80 million ash trees in the UK.
RNA analysis (of infected lesion)
In December 2012, results were made publicly available by a laboratory in Norwich (UK) from the sequencing of active genetic molecules (called “RNA transcripts”) isolated from an ash dieback infected lesion on the twig of an ash tree. This analysis provided data on the fungal genes that were switched on – although the genetic sequences published were likely to have also contained sequences from the ash tree’s cells and possibly from other infecting organisms. At least 30% of the sequences did appear to be fungal in origin when checked for similarity (e.g. using complex DNA/RNA sequence matching programs such as “BLAST”). One of the most interesting active fungal genes identified, encodes (i.e. makes) a protein toxin called NLP that is similar to a group of “actinoporin” toxins.
DNA analysis (Chalara fungus genome sequencing)
In March 2013, a further advance was made. The DNA genome of the fungus was sequenced (i.e. fully worked out) by the same laboratory. The results have been made available to others via a website. Several genes have been identified that encode toxins that may cause the necrosis (death) of tree tissue.
The genome of this fungus, found in the UK, is being compared to the DNA of other isolates of the fungus from across Europe.
Genome sequencing of the British ash tree was started in January 2013. Its size is 954 million base pairs (which is just under a third of the size of the human genome).
The genetic basis of the resistance of a minority of Danish ash trees to the fungus will eventually be explored. These trees, which are known as Tree 35 and constitute just 2% of ash trees in Denmark, have survived the epidemic. It may be possible to identify the important genes (or the variants contained in them) that confer this resistance and perhaps to begin selective breeding programs to produce a new generation of resistant ash trees.