A PATHOGEN-INDUCED GENE OF BARLEY ENCODES A HSP90 HOMOLOG SHOWING STRIKING SIMILARITY TO VERTEBRATE FORMS RESIDENT IN THE ENDOPLASMIC-RETICULUM

The full-length nucleotide sequence of a barley (Hordeum vulgare L.) l eaf mRNA, found to increase rapidly in amount during infection attempt s by the powdery mildew fungus (Erysiphe graminis DC. ex Merat), is re ported. The mRNA encodes a polypeptide of 809 amino acid residues whic h, by sequence comparison, was identified as a member of the 90 kDa he at shock protein (HSP90) family. The encoded protein most resembles th e endoplasmic reticulum (ER) resident HSP90 protein, the 94 kDa glucos e-regulated protein (GRP94) of vertebrates, as it possesses both the c haracteristic N-terminal domain including a signal peptide sequence an d the C-terminal ER retention signal (Lys-Asp-Glu-Leu). A transcript c ross-hybridizing at high stringency accumulated rapidly in leaves upon heat shock treatment. Genomic DNA blot analysis indicated the presenc e of a family of related genes in the barley genome.