Differentiation-specific genes of rust fungi have limited distribution among fungi

The infection-structure (INF) genes from Uromyces appendiculatus (bean rust fungus) are related to formation of the infection structures. To determine if these genes have homologs in other fungi, genomic DNAs from selected Ascomycetes and Basidiomycetes were probed with fragments of INF24 and INF56. At high stringency, INF24 hybridized strongly with DNA from U. appendiculatus, but only weakly with DNA from P. graminis tritici; and hybridization was not detected with DNA from U. vignae (cowpea rust fungus). In contrast, INF56 hybridized with DNA from U. appendiculatus and U. vignae but not with DNA from P. graminis tritici. UAM, a constitutively expressed gene from P. graminis tritici, hybridized with DNA from all three species of rust fungi. At high stringency, none of the probes hybridized with DNA from nonrust fungi, but at low stringency, INF56 hybridized weakly with DNA from most of them. In general, the results suggest that the rust genes are not broadly conserved among the fungi.