DIFFERENTIAL GENE TRANSCRIPT ACCUMULATION IN BARLEY LEAF EPIDERMIS AND MESOPHYLL IN RESPONSE TO ATTACK BY BLUMERIA-GRAMINIS F-SP HORDEI (SYN. ERYSIPHE-GRAMINIS F-SP HORDEI)

A number of barley cDNAs isolated by differential screening represent gene transcripts which accumulate during fungal pathogen attack. The e ncoded proteins comprise species commonly encountered in plant-pathoge n interactions, e.g. PR proteins, but also protein species not previou sly reported from plant-pathogen interactions: a novel flavonoid O-met hyltransferase, a 14-3-3 protein, an endoplasmatic chaperone (GRP94), an oxalate oxidase, an oxalate oxidase-like protein, and some species with no known homologues. One of these latter sequences BH72-Q3, encod ing a small proline-rich protein, is presented here. Transcripts of 15 gene families accumulated in the leaves following inoculation with Bl umeria graminis f.sp. hordei (syn. Erysiphe graminis Esp. hordei) in b oth compatible and incompatible interactions. During the first 24 h af ter inoculation no clear differences were observed among different int eraction types. At later stages transcript accumulation reflected the different infection types, with strong late accumulation in compatible interactions, a somewhat earlier accumulation in an incompatible mult i-cell HR interaction, and only weak accumulation in an incompatible s ingle cell HR interaction. Experiments using isolated epidermal strips and the residual mesophyll material showed that the oxalate oxidase-l ike gene transcript accumulated exclusively in the epidermis, whereas the 14-3-3, GRP94, and BH6-12 transcripts accumulated in both epidermi s and mesophyll. All other gene transcripts appeared to accumulate pre ferentially in the mesophyll cells, however, with increased epidermal accumulation late after inoculation. The exception is the oxalate oxid ase transcript, which accumulated exclusively in the mesophyll. The re sponse of the barley plant to attack by the mildew fungus thus appears to consist of a complex of interconnected reactions in the epidermis and the underlying mesophyll cells. (C) 1997 Academic Press Limited.