The transition metal chelator nicotianamine is synthesized by filamentous fungi

Nicotianamine is an important metal ligand in plants. Surprisingly, recent genome sequencing revealed that ascomycetes encode proteins with similarity to plant nicotianamine synthases (NAS). By expression in a Zn2+-hypersensitive fission yeast mutant we show for a protein from Neurospora crassa that it indeed possesses NAS activity. Using electrospray-ionization-quadrupole-time-of-flight mass spectrometry we prove the formation of nicotianamine in N. crassa. Transcript level is strongly upregulated under Zn deficiency as shown by real-time PCR. These findings demonstrate that nicotianamine is more widespread in nature than anticipated and provide further evidence for a function of nicotianamine as a cytosolic chelator of Zn2+ ions.