Differential gene transcript accumulation in barley leaf epidermis and mesophyll in response to attack byBlumeria graminisf.sp.hordei(syn.Erysiphe graminisf.sp.hordei)

Abstract

A number of barley cDNAs isolated by differential screening represent gene transcripts which accumulate during fungal pathogen attack. The encoded proteins comprise species commonly encountered in plant–pathogen interactions, e.g. PR proteins, but also protein species not previously reported from plant-pathogen interactions: a novel flavonoidO-methyltransferase, 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, encoding a small proline-rich protein, is presented here. Transcripts of 15 gene families accumulated in the leaves following inoculation withBlumeria graminisf.sp.hordei(syn.Erysiphe graminisf.sp.hordei) in both compatible and incompatible interactions. During the first 24 h after inoculation no clear differences were observed among different interaction 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 multi-cell HR interaction, and only weak accumulation in an incompatible single cell HR interaction. Experiments using isolated epidermal strips and the residual mesophyll material showed that the oxalate oxidase-like gene transcript accumulated exclusively in the epidermis, whereas the 14-3-3, GRP94, and BH6-12 transcripts accumulated in both epidermis and mesophyll. All other gene transcripts appeared to accumulate preferentially in the mesophyll cells, however, with increased epidermal accumulation late after inoculation. The exception is the oxalate oxidase transcript, which accumulated exclusively in the mesophyll. The response 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.