Rice blast fungus sequenced

Rice (Oryza sativa L.) is a major staple food crop for half of the world’s population. The International Rice Research Institute, Philippines, estimates that in order to feed the growing global population, rice production must increase by another one-third by the year 2020. Magnaporthe grisea (anamorph, Pyricularia oryzae) causes rice blast disease (Figure 1) and is the most destructive pathogen of rice worldwide; around 50% of production may be lost in a field moderately affected by infection. Each year the fungus destroys rice enough to feed an estimated 60 million people. The disease is currently managed using resistant cultivars, fungicides and cultural practices. Strains of this fungus have also been reported to infect wheat, barley and turf grass. Most of the rice cultivars are susceptible to some strain of this fungus and since the pathogen is highly variable, breeding for durable resistance to blast remains a major challenge. The rice blast fungus has emerged as a model system for the study of plant– pathogen interactions. This is largely due to the efforts of a small community of researchers worldwide, who have developed the necessary tools for molecular biological investigations in this fungus. The mechanism of plant infection by M. grisea is currently better understood than for any other cereal disease. Infection by the rice blast fungus starts when the three-celled conidia from conidiophores land on a host leaf and anchor the leaf cuticle with the help of spore-tip mucilage. Germination proceeds with the extension of germ tube, which undergoes hooking and swelling at its tip and then differentiates into a melanized infection structure called ‘appressorium’. The formation of this infection structure on the host surface marks the onset of the disease (Figure 2). Publication of the draft sequence of this fungus being the first such sequence from a fungal pathogen of an economically important crop plant is a welcome addition to the list of sequenced genomes. The genome was sequenced by International Rice Blast Genome Consortium with participating laboratories from USA, UK, France and Korea. Sadly, there was no Indian participation in this effort, even though rice blast remains a major challenge for this country. The availability of the genome sequence will provide an enormous impetus to better understanding the molecular basis of fungal disease development in plants. The genome of M. grisea is around 40 Mb, distributed among seven chromosomes. The draft sequence predicts 11,109 genes, with a frequency of 1 gene every 3.5 kb in the rice blast genome. This information will facilitate a systematic characterization of pathogen-specific genes and the study of the biology of this fungus. The genome of M. grisea possesses more genes compared to the non-pathogenic Neurospora crassa and Aspergillus niger,