S5H/DMR6 Encodes a Salicylic Acid 5-Hydroxylase That Fine-Tunes Salicylic Acid Homeostasis

Journal Article · Tue Sep 12 00:00:00 EDT 2017 · Plant Physiology (Bethesda)

DOI:https://doi.org/10.1104/pp.17.00695· OSTI ID:1389878

Zhang, Yanjun  ^[1]; Zhao, Li ^[1]; Zhao, Jiangzhe ^[1]; Li, Yujia ^[1]; Wang, Jinbin ^[1]; Guo, Rong ^[1]; Gan, Susheng ^[2]; Liu, Chang-Jun  ^[3]; Zhang, Kewei  ^[1]

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1. Institute of Plant Genetics and Developmental Biology, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua, Zhejiang 321004, China
2. Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853
3. Department of Biosciences, Brookhaven National Laboratory, Upton, New York 11973

The phytohormone salicylic acid (SA) plays essential roles in biotic and abiotic responses, plant development, and leaf senescence. 2,5-Dihydroxybenzoic acid (2,5-DHBA or gentisic acid) is one of the most commonly occurring aromatic acids in green plants and is assumed to be generated from SA, but the enzymes involved in its production remain obscure. DMR6 (Downy Mildew Resistant 6, At5g24530) has been proven essential in plant immunity of Arabidopsis, but its biochemical properties are not well understood. Here in this paper, we report the discovery and functional characterization of DMR6 as a SA 5-hydroxylase (S5H) that catalyzes the formation of 2,5-DHBA by hydroxylating SA at the C5 position of its phenyl ring in Arabidopsis. S5H/DMR6 specifically converts SA to 2,5-DHBA in vitro and displays higher catalytic efficiency (K_cat/K_m=4.96×10⁴ M^-1s^-1) than the previously reported SA 3-hydroxylase (S3H, K_cat/K_m=6.09 × 10³ M^-1s^-1) for SA. Interestingly, S5H/DMR6 displays a substrate inhibition property that may enable automatic control of its enzyme activities. The s5h mutant and s5hs3h double mutant over accumulate SA and display phenotypes such as a smaller growth size, early senescence and a loss of susceptibility to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). S5H/DMR6 is sensitively induced by SA/pathogen treatment and is widely expressed from young seedlings to senescing plants, whereas S3H is more specifically expressed at the mature and senescing stages. Collectively, our results disclose the identity of the enzyme required for 2,5-DHBA formation and reveal a mechanism by which plants fine-tune SA homeostasis by mediating SA 5-hydroxylation.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Natural Science Foundation of China (NSFC); Natural Science Foundation of Zhejiang Province
• Grant/Contract Number: DEAC0298CH10886 (BO-169); SC0012704; AC02-98CH10886
• OSTI ID: 1389878
• Alternate ID(s): OSTI ID: 1412669
• Report Number(s): BNL-114465-2017-JA; /plantphysiol/175/3/1082.atom
• Journal Information: Plant Physiology (Bethesda), Journal Name: Plant Physiology (Bethesda) Vol. 175 Journal Issue: 3; ISSN 0032-0889
• Publisher: Oxford University Press
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES