Ric1, a Phytophthora infestans gene with homology to stress-induced genes

From a set of Phytophthora infestans cDNA clones that were randomly selecte d from a potato-P. infestans interaction cDNA library, a relatively high pr oportion (5 out of 22) appeared to be derived from the same gene. The gene was designated ric1. P. infestans contains two copies of ric1 which share 9 8% homology at the nucleotide-sequence level and 100% at the aminoacid leve l. The nucleotide sequence predicts an open reading frame of 171 bp encodin g a 57 amino-acid hydrophobic-peptide with two potential membrane-spanning domains. The predicted peptide shows high homology to a peptide encoded by plant genes whose expression is specifically induced during stress conditio ns. Southern-blot analysis of genomic DNA of several Phytopophthora species indicated that most species contain lid homologues. During the life cycle of P. infestans, rid was expressed in all developmental stages but the leve l of expression varied. Sporangia and germinating cysts appeared to contain only very little ric1 mRNA whereas in the mycelium and during in planta gr owth higher levels were detected. Subjecting the mycelium to osmotic stress or to a high pH resulted in increased ric1 expression.