PRODUCTION OF A MATING INHIBITOR BY USTILAGO-HORDEI

Ustilago hordei, the cause of barley covered smut, was found to produc e a factor that inhibited its own mating. The mating inhibition Factor (MIF) specifically inhibited mating of U. hordei and other Ustilago s pp., but not teliospore germination or sporidial growth. MIF did preve nt teliospore germination of Tilletia caries and I: contraversa. MIF w as found at low levels in culture supernatants of either mating type o f ii. hordei grown separately but at higher levels when both mating ty pes were grown together, in the supernatants of MAT-I mating type cell s transformed with the MAT-I pheromone gene mfal and of MAT-2 cells tr ansformed with either mfal or the MAT-I pheromone receptor gene pra1. Diploid cells produced no detectable inhibitor, nor did MAT-I cells wi th a disrupted mating type locus that deleted both mfal and pra1. MIF production was restored when mfal, but nor pra1, was added back to the MAT-1 Delta cells. MIF activity was altered by protease treatment. Hi ghly purified MIF from MAT-I cells contained cysteine methyl ester, fa rnesyl cysteine, farnesyl cysteine methyl ester, and a dodecapeptide w ith a mass consistent with that of MAT-I pheromone lacking the termina l cysteine. Since smut fungi must first mate to become pathogenic, mat ing inhibition has the potential to be an effective method of disease control far these pathogens.