• The first species for which the genome is entirely sequenced at the CRG.
  
• The study sequenced the genome of two strains of P. digitatum to find out why it is so specific and virulent, in addition to its varying ability to resist antifungal compounds
  
• The study was undertaken by researchers from the CRG and IATA-CSIC and was published in December in the journal BMC Genomics.

Researchers from the Centre for Genomic Regulation (CRG) and the Institute of Agrochemistry and Food Technology (IATA-CSIC), Valencia, have published the genome sequence of the fungus known as citrus green mould (Penicillium digitatum). The work, which represents the first species for which the genome has been entirely sequenced at the CRG, will enable, among other things, an understanding of the molecular basis for its resistance to pesticides and alternative methods to minimise the financial losses caused by this mould. In addition, these fungi are often a source of natural compounds with antimicrobial activity, such as penicillin, and having the genome available should help in their detection.
The scientists have sequenced the complete genome of two varieties of P. digitatum with different fungicide resistance, in order to understand the enormous infection capacity of this fungus and its high specificity, as it is only found on citrus fruit.
Green mould is well known in all households. It occurs on ripe food if it is not eaten in time, and is one of the most important causes of financial waste. Food travels from the field to our table, a journey that can also result in losses. This fungus is the cause of almost 90% of citrus wastage caused by putrefaction. The mould only affects this type of fruit and is a real headache for citrus farmers and traders both in Spain and other parts of the world.
“Our comparisons with partial sequences obtained in countries including China and Japan suggest that this species has spread worldwide very recently, and that resistance to fungicides is caused by only a few mutations which, once created, can propagate globally, perhaps taking advantage of international trade routes”, asserts Toni Gabaldón, head of the CRG Comparative Genetics group and co-author of the study. “By sequencing its genome, we have been able to find mutations that confer resistance to fungicides, something which will enable us to explore possible solutions to this growing problem”.
Also very interesting are the secondary compounds produced by this organism. Fungi of the genus Penicillium produce highly active antibacterial compounds which they use to eliminate competitors in their natural environment and which may have clinical application. The famous antibiotic penicillin is an example of one of these compounds. P. digitatum does not produce penicillin but the analysis of its genome has provided an insight into other genes which may be able to synthesise different antibacterial compounds.
The IATA researchers in Valencia will undertake laboratory studies on these candidate genes. Meanwhile, the CRG group will continue to collaborate with other sequencing studies such that for Penicillium expansum, a relative of P. digitatum which only affects apples. The ultimate aim is to understand the causes of this high level of specificity.
The work was partly financed by the Spanish Ministry of Economy and Competitiveness.
Reference: Marcet-Houben et al. Genome sequence of the necrotrophic fungus Penicillium digitatum, the main postharvest pathogen of citrus. BMC Genomics 2012, 13:646. doi:10.1186/1471-2164-13-646
Photos: Penicillium digitatum
Other references: Time-lapse video showing the infection of a lemon by P. digitatum, over a period of 12 days (Cornell University).  http://youtu.be/W1Bzi7T8-HQ
Further information: Juan Manuel Sarasua – CRG Press Officer – 933160153