|Navarre, Duroy - Roy|
|Del Pozo, O|
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2002
Publication Date: 8/15/2002
Citation: Slaymaker, D.H., Navarre, D.A., Clark, D., Del Pozo, O., Martin, G.G., Klessig, D.F. 2002. The tobacco salicylic acid-binding protein 3 (SABP3) is the chloroplast carbonic anhydrase, which exhibits antioxidant activity and plays a role in the hypersensitive defense response. Proceedings of the National Academy of Sciences USA. 99(18):11640-11645. Epub 2002 Aug 15. Interpretive Summary: Salicylic acid plays a key role in regulating plant defense responses, however the mechanism(s)by which SA regulates defense responses is not yet clear.This work identifies a novel salicylic acid-binding protein located in chloroplasts as carbonic anhydrase (CA). The work suggests that CA may be a bifunctional protein with an additional function beyond its known role eand have an important anti-oxidant function.
Technical Abstract: In plants, salicylic acid (SA) plays an important role in signaling both local and systemic defense responses. Previous efforts to identify SA effector proteins in tobacco have led to the isolation of two soluble cytoplasmic SA-binding proteins: catalase (SABP) and an approximately 25 kDa protein, SABP2. Here we describe the identification of an SA-binding protein, SABP3, in the stroma of tobacco chloroplasts. SABP3 bound SA with an apparent dissociation constant (Kd) of 3.7 mM and exhibited much greater affinity for biologically active SA analogs than inactive analogs. Purification and partial sequencing of SABP3 indicated that it is the chloroplast carbonic anhydrase (CA). Confirming this finding, recombinant tobacco chloroplast CA exhibited both CA enzymatic and SA-binding activities. Expression of this protein in yeast also demonstrated that CA/SABP3 has antioxidant activity. A second gene encoding CA was also cloned and its encoded protein was shown to behave similar to that purifie as SABP3. These results demonstrate that SA may act through multiple effector proteins in plants, and sheds further light on the function of CA in chloroplasts.