Transient expression of members of the germin-like gene family in epidermal cells of wheat confers disease resistance

The wheat genome encodes a family of germin-like proteins that differ with respect to regulation and tissue specificity of expression of the correspon ding genes. While germin exhibits oxalate oxidase (E.C. 1.2.3.4.) activity, the germin-like proteins (GLPs) have no known enzymatic activity. A role o f oxalate oxidase in plant defence has been proposed, based on the capacity of the enzyme to produce H2O2. a reactive oxygen species. The role in defe nce of germin and other members of the germin-like gene family was function ally assessed in a transient assay system based on particle bombardment of wheat leaves. Transient expression of the pathogen-induced germin gf-2.8 ge ne, but not of the constitutively expressed HvGLP1 gene, reduced the penetr ation efficiency of Blumeria (syn. Erysiphe) graminis f.sp. tritici. the ca usal agent of wheat powdery mildew, on transformed cells. Two engineered ge rmin-gf-2.8 genes and the TaGLP2a gene, which all encoded proteins without oxalate oxidase activity, also reduced the penetration efficiency of the fu ngus, demonstrating that oxalate oxidase activity is not required for confe rring enhanced resistance. Instead. activity tagging experiments showed tha t in cells transiently expressing the germin gf-2.8 gene, the transgene pro duct became insolubilised at sites of attempted fungal penetration where lo calised production of H2O2 was observed. Thus. germin and GLPs may play a s tructural role in cell-wall re-enforcement during pathogen attack.