The genomes of mycosphaerella graminicola and M. Fijiensis

Abstract

Mycosphaerella graminicola (synonym: Zymoseptoria tritici) and Mycosphaerella fijiensis in the Ascomycetes order Capnodiales are economically important pathogens causing Septoria tritici blotch of wheat and black Sigatoka or leaf streak of banana, respectively. Both diseases occur wherever their respective crops occur worldwide and have been difficult to control due to lack of effective resistance in the host plants and the development of fungicide insensitivity in populations of the pathogens. The 39.7-Mb genome of M. graminicola was sequenced completely and consists of 13 core chromosomes plus a dispensome of eight small chromosomes that differ from those in the core and probably originated by horizontal transfer from an unknown donor more than 10,000 years ago. The genome of M. fijiensis was much larger at 74.1 Mb, primarily due to proliferation of class I retrotransposons. It also may contain dispensable chromosomes that are different from those in M. graminicola. Both species contain a reduced set of genes for cell wall degrading enzymes compared to other plant-pathogenic fungi and possibly degrade proteins rather than carbohydrates during the biotrophic phase of infection. Interestingly, the genome of M. fijiensis contained effectors that are functionally similar to those seen in the related tomato pathogen, Cladosporium fulvum, and can be recognized by the corresponding tomato resistance genes. These effectors may be useful for future breeding of resistant banana cultivars and could help to identify sources of nonhost resistance from other crop species.