Poster: Plant-pathogen interactions

Abs # 563: Identification of a SA receptor required for plant innate immunity

Presenter:	Kumar, Dhirendra , dk237@cornell.edu
Authors	Kumar, Dhirendra  (A)   Vlot, Anna C. (A)   Kang, Hong G. (A)   Zhou, Fasong  (A)   Klessig, Daniel F. (A)
Affiliations:	(A): Boyce Thompson Institute for Plant Research

Salicylic acid (SA) is a critical hormone for signaling innate immunity in plants. While investigating how SA exerts its effects, several putative effector proteins have been identified in tobacco including catalase, ascorbate peroxidase and carbonic anhydrase. All three bind SA with low to moderate affinity (K_d of 14-3.7 μM). Another SA-binding protein identified was SABP2. It is present in low abundance and binds SA with highest affinity (K_d=90nM) of all the SA-binding proteins identified. It was purified 24,000 fold from tobacco leaves and its encoding gene was cloned. Recombinant SABP2 exhibits high affinity for SA, which can be competed by addition of active but not inactive analogs of SA. Sequence analysis predicted that SABP2 is a lipase belonging to the α/β fold hydrolase super family. Confirming this prediction, recombinant SABP2 exhibited lipase activity against several synthetic substrates. Moreover, this activity was stimulated by SA binding. Silencing of SABP2 expression suppressed local resistance to TMV, induction of PR-1 gene expression by SA and more importantly development of systemic acquired resistance. Together, these results suggest that SABP2 is an SA receptor that is required for the plant immune response.