2012 Annual Report 1a.Objectives (from AD-416): 1) Nematode CLE variable domain function, and. 2)nematode CLE processing activity in planta. 1b.Approach (from AD-416): Using agrobacterium-mediated transient expression systems to investigate nematode CLE processing in planta. 3.Progress Report: Plant-parasitic cyst nematodes produce secreted effector proteins that function as peptide mimics of plant CLE peptides hypothesized to play a role in the developmental reprogramming of root cells to form specialized feeding cells. Studies detail the cellular targeting and functional domains of nematode and plant CLE proteins in a comparative analysis. Research presents evidence to indicate that nematode CLE proteins are delivered to the cytoplasm of feeding cells, but function in the extracellular space, consistent with their proposed role as mimics of plant CLE peptides. The results demonstrated that both the variable domain (VD) and CLE motifs are required for their function in planta. Furthermore, unlike plant CLEs, the nematode CLE VD functions in the host-specific recognition and is sufficient to traffic cytoplasmically delivered CLEs to the apoplast. Ithaca researchers have acquired evidence that nematode CLEs can be recognized by plant cellular machinery to be further modified and processed into biologically active CLE peptides when delivered into host plant cells to function as mimics of endogenous plant CLE peptides. Moreover, the data also suggests that nematode CLE proteins are subject to host-specific processing. The identification and characterization of CLE-like genes from the beet cyst nematode (BCN), a parasite of the model plant Arabidopsis, has enabled the use of the BCN-Arabidopsis model pathosystem to identify the plant receptors of nematode CLEs accelerating studies to elucidate the role of nematode CLE peptides in feeding cell formation.