Genomes contain a large number of unique genes which have not been found in 
other species. Although the origin of such "orphan" genes remains unclear, they 
are thought to be involved in species-specific adaptive processes. Here, we 
analyzed seven orphan genes (MoSPC1 to MoSPC7) prioritized based on in planta 
expressed sequence tag data in the rice blast fungus, Magnaporthe oryzae. 
Expression analysis using qRT-PCR confirmed the expression of four genes 
(MoSPC1, MoSPC2, MoSPC3 and MoSPC7) during plant infection. However, individual 
deletion mutants of these four genes did not differ from the wild-type strain 
for all phenotypes examined, including pathogenicity. The length, GC contents, 
codon adaptation index and expression during mycelial growth of the four genes 
suggest that these genes formed during the evolutionary history of M. oryzae. 
Synteny analyses using closely related fungal species corroborated the notion 
that these genes evolved de novo in the M. oryzae genome. In this report, we 
discuss our inability to detect phenotypic changes in the four deletion mutants. 
Based on these results, the four orphan genes may be products of de novo gene 
birth processes, and their adaptive potential is in the course of being tested 
for retention or extinction through natural selection.