Minisymposium 18: Plant defense signaling
Abs #
33003: Identification of a SA receptor required for plant innate immunity
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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
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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 (Kd of 14-3.7uM). Another SA-binding protein identified was SABP2. It is present in low abundance and binds SA with highest affinity (Kd=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 hydrolase super family. Confirming this prediction, recombinant SABP2 exhibited lipase activity against several synthetic substrates. Moreover, this activity was stimulated by SA binding. To assess the role of SABP2 in defense signaling, SABP2 expression was silenced by using RNA interference (RNAi). SABP2-silenced plants when inoculated with TMV, developed larger lesions and allowed greater viral replication. SA induction of PR-1 expression, which is associated with resistance to TMV, was also suppressed in the SABP2-silenced plants. Silencing of SABP2 showed more pronounced effect in the development of systemic acquired resistance (SAR). In control plants, the lesions formed on the secondary inoculated leaves were 50% smaller than those developed after primary infection. The reduction in secondary lesion size is a common marker for SAR. By contrast, the lesions formed by secondary inoculations on the SABP2-silenced plants developed as large as those formed after a primary infection and 2.5-fold larger than those exhibited by control plants. In the SABP2-silenced plants, systemic expression of the PR-1 gene, a common marker for SAR, was also reduced. Together, these results suggest that SABP2 is an SA receptor that is required for the plant immune response.
