Figure 1.

NDR1 plays multiple roles in cell physiology and pathogen defense signaling. NDR1 (NON-RACE SPECIFIC DISEASE RESISTANCE-1) is a plasma membrane localized, GPI-anchored protein that is capable of forming homodimers. NDR1 contains an NGD (Asn-Gly-Asp) motif located in the putative apoplastic-localized region of the protein, which has been shown to be important for maintaining cell wall-plasma membrane adhesion points⁹ though either direct (1) or indirect (2) interaction with components of the cell wall. Additional cellular components mediating this connection are as of yet unknown. The role of NDR1 in ETI had been further strengthened through the identification of an interaction between NDR1 and RIN4 (RPM1 INTERACTING PROTEIN 4).⁸ RIN4 has been shown to associate with theR-protein, RPS2 (RESISTANCE TO PSEUDOMONAS SYRINGAE2),²⁶ and it is through RIN4's cleavage by the P. syringae DC3000 effector protein AvrRpt2 and the subsequent recognition of this event by RPS2, that ETI is activated. Recently, NDR1 has been directly linked to the initiationof the MAPK (MITOGEN ACTIVATED PROTEIN KINASE) pathway and PTI (PAMP Triggered Immunity). Although the specific interaction of NDR1 in the upstream components of PTI signaling is unknown (3), NDR1 is required for proper activation of the MAPK signal cascade. ETI, effector triggered immunity; PTI, PAMP triggered immunity.