The extremely conserved pyroA gene of Aspergillus nidulans is required forpyridoxine synthesis and is required indirectly for resistance to photosensitizers

Numerous disparate studies in plants, filamentous fungi, yeast, Archaea, an d bacteria have identified one of the most highly conserved proteins (SNZ f amily) for which no function was previously defined. Members have been impl icated in the stress response of plants and yeast and resistance to singlet oxygen toxicity in the plant pathogen Cercospora, However, it is found in some anaerobic bacteria and is absent in some aerobic bacteria. We have clo ned the Aspergillus nidulans homologue (pyroA) of this highly conserved gen e and define this gene family as encoding an enzyme specifically required f or pyridoxine biosynthesis. This realization has enabled us to define a sec ond pathway for pyridoxine biosynthesis. Some bacteria utilize the pdx pyri doxine biosynthetic pathway defined in Escherichia coli and others utilize the pyroA pathway. However, Eukarya and Archaea exclusively use the pyroA p athway. We also found that pyridoxine is destroyed in the presence of singl et oxygen, helping to explain the connection to singlet oxygen sensitivity defined in Cercospora, These data bring clarity to the previously confusing data on this gene family. However, a new conundrum now exists; why have hi ghly related bacteria evolved with different pathways for pyridoxine biosyn thesis?.