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BAH1/NLA, a RING-Type Ubiquitin E3 Ligase, Regulates the Accumulation of Salicylic Acid and Immune Responses to Pseudomonas syringae DC3000^1,[W],[OA]

Department of Biology, Faculty of Sciences, Kyushu University, Hakozaki, Fukuoka 812–8581, Japan

Salicylic acid (SA) is a primary factor responsible for exerting diverse immune responses in plants and is synthesized in response to attack by a wide range of pathogens. The Arabidopsis (Arabidopsis thaliana) sid2 mutant is defective in a SA biosynthetic pathway involving ISOCHORISMATE SYNTHASE1 (ICS1) and consequently contains reduced levels of SA. However, the sid2 mutant as well as ICS-suppressed tobacco (Nicotiana benthamiana) still accumulate a small but significant level of SA. These observations along with previous studies suggest that SA might also be synthesized by another pathway involving benzoic acid (BA). Here we isolated a benzoic acid hypersensitive1-Dominant (bah1-D) mutant that excessively accumulated SA after application of BA from activation-tagged lines. This mutant also accumulated higher levels of SA after inoculation with Pseudomonas syringae pv tomato DC3000. Analysis of the bah1-D sid2 double mutant suggested that the bah1-D mutation caused both ICS1-dependent and -independent accumulation. In addition, the bah1-D mutant showed SA-dependent localized cell death in response to P. syringae pv tomato DC3000. The T-DNA insertional mutation that caused the bah1-D phenotypes resulted in the suppression of expression of the NLA gene, which encodes a RING-type ubiquitin E3 ligase. These results suggest that BAH1/NLA plays crucial roles in the ubiquitination-mediated regulation of immune responses, including BA- and pathogen-induced SA accumulation, and control of cell death.

² Present address: RIKEN Plant Science Center, Yokohama 230–0045, Japan.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Koh Iba (koibascb{at}mbox.nc.kyushu-u.ac.jp).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.124529

^* Corresponding author; e-mail koibascb{at}mbox.nc.kyushu-u.ac.jp.

Received June 10, 2008; accepted August 25, 2008; published August 27, 2008.