In plants, defensive proteins secreted to leaf aerial surfaces have not previously been considered to be a strategy of pathogen resistance, and the general occurrence of leaf surface proteins is not generally recognized. We found that leaf water washes of the experimental plant Nicotiana tabacum 'TI 1068' contained highly hydrophobic, basic proteins that inhibited spore germination and leaf infection by the oomycete pathogen Peronospora tabacina . We termed these surface-localized proteins tobacco phylloplanins, and we isolated the novel gene T-Phylloplanin and its promoter from N. tabacum . Escherichia coli -expressed T-phylloplanin inhibited P. tabacina spore germination and greatly reduced leaf infection. The T-phylloplanin promoter, when fused with the reporter genes ß-glucuronidase and green fluorescent protein, directed biosynthesis only in apical-tip cell clusters of short, procumbent glandular trichomes (SGTs). Here we provide evidence for a protein-based surface defense system in the plant kingdom, wherein protein biosynthesis in SGTs allows surface secretion and deposition of defensive phylloplanins on aerial surfaces as a first-point-of-contact deterrent to pathogen establishment. Phylloplanins were detected on all tobaccos examined thus far, except N. glauca . As yet uncharacterized surface proteins have been detected on most plant species examined.