In tobacco and other species of the genus Nicotiana , resistance to P. infestans is diverse and the HR varies in intensity depending on the plant species examined. P. infestans as well as other Phytophthora species produce 10 kD extracellular proteins, known as elicitins , that induce the HR and other biochemical changes associated with defense responses in Nicotiana . Therefore, these atypical INF proteins may be surface or cell wall associated glycoproteins that interact with plant cells during infection. Schematic illustration of the INF elicitin family of P. infestans . The four main domains correspond to the signal peptide, elicitin domain, C-terminal domain, and transmembrane domain, respectively.
Vertical bars refer to the conserved cysteine residues.
Black boxes in the INF7 elicitin domain refer to deletions. Our results suggest that multiple layers of INF elicitin recognition and late blight resistance occur in Nicotiana . We are now performing qualitative and quantitative dissection of these layers of nonhost resistance into specific R gene-inf elicitin interactions by using a combination of in planta functional assays of INF elicitor activities, analysis of abundance and localization of inf transcripts and INF proteins, and construction of P. infestans strains deficient in INF proteins. One objective of our research is to exploit the rapidly accumulating genomics data to identify novel elicitor proteins from Phytophthora .