DEFENSE-RELATED GENE ACTIVATION DURING AN INCOMPATIBLE INTERACTION BETWEEN STAGONOSPORA (SEPTORIA) NODORUM AND BARLEY (HORDEUM-VULGARE L) COLEOPTILE CELLS

Two previously unidentified cDNA clones (bsi1 and bpr1-1) were isolate d by differential hybridization from a cDNA library of Stagonospora (S eptoria) nodorum (Berk) Castellani & E.G. Germane (teleomorph Phaeosph aeria (Leptosphaeria) nodorum (E. Muller) Hedjaroude-challenged barley (Hordeum vulgare L.) coleoptiles. bsi1 encoded a cysteine-rich protei n containing 89 amino acids (aa) with a relative molecular mass (M(r)) of 9405. Protein sequence homologies showed that Bsi1 was very simila r to an aluminium-induced protein from wheat and indicated that it was related to the Bowman-Birk-type proteinase inhibitors (BB-PIs). The p redicted aa sequence of Bsi1 contained an N-terminal secretory signal sequence which implied that the protein was exported. The other clone, bpr1-1, which was truncated at the 5' end, encoded a type-1 pathogene sis-related (PR-1) protein. The complete sequence of bpr1-1 was obtain ed after cloning a barley genomic DNA fragment and was shown to encode a basic protein containing 174 aa with a M(r) of 18 859. The deduced aa sequence of bpr1-1 contained both an N-terminal secretory signal se quence and a charged C-terminal extension. This latter sequence may re present a vacuolar targeting signal. bsi1 and bpr1-1 and four other de fence-related genes (encoding 1,3-beta-glucanase, 3-hydroxy-3-methylgl utaryl-coenzyme A (HMG-CoA) reductase, a homologue of a putative wheat peroxidase, and barley leaf-specific thionin), showed increased trans cription levels in S. nodorum-challenged coleoptiles, although their p attern of accumulation varied after inoculation (a.i.). The potential role of these induced genes in defence against fungal attack is discus sed.