Expression of thaumatin-like permatin PR-5 genes switches from the ovary wall to the aleurone in developing barley and oat seeds

Permatins are antifungal thaumatin-like proteins (TLPs) of the PR-5 family of pathogenesis-related proteins. They occur in many cereals, but little is known of their expression and roles. Permatin cDNA clones were produced an d used to study expression in developing barley and oat seeds. Actin and CD C48 mRNAs declined rapidly following inoculation of barley spikes with Fusa rium graminearum, Despite this, permatin mRNA levels remained constant or i ncreased slightly. Studies of permatin gene expression in healthy plants re vealed that developing barley and oat seeds accumulate permatin mRNA in an unusual bimodal pattern. Permatin mRNA and protein are highly abundant arou nd the time of pollination and then decrease rapidly to near-zero. A second peak occurs in the doughy stage of development. Antibody and DNA probe hyb ridization studies showed that expression initially occurs in the ovary wal l and then switches to the aleurone and ventral furrow of developing seeds, reaching a peak in the doughy stage. Small amounts of permatin mRNAs also occur in certain vegetative tissues. The barley and oat permatin sequences provided sufficient comparisons between cereal TLPs to suggest that deletio ns or additions in specific elements could have led to the divergence of le af- and seed-specific TI-Ps. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.