title: Salicylic acid 3-hydroxylase regulates Arabidopsis leaf longevity by mediating salicylic acid catabolism.
abstract: The plant hormone salicylic acid (SA) plays critical roles in plant defense, stress responses, and senescence. Although SA biosynthesis is well understood, the pathways by which SA is catabolized remain elusive. Here we report the identification and characterization of an SA 3-hydroxylase (S3H) involved in SA catabolism during leaf senescence. S3H is associated with senescence and is inducible by SA and is thus a key part of a negative feedback regulation system of SA levels during senescence. The enzyme converts SA (with a Km of 58.29 µM) to both 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-DHBA in vitro but only 2,3-DHBA in vivo. The s3h knockout mutants fail to produce 2,3-DHBA sugar conjugates, accumulate very high levels of SA and its sugar conjugates, and exhibit a precocious senescence phenotype. Conversely, the gain-of-function lines contain high levels of 2,3-DHBA sugar conjugates and extremely low levels of SA and its sugar conjugates and display a significantly extended leaf longevity. This research reveals an elegant SA catabolic mechanism by which plants regulate SA levels by converting it to 2,3-DHBA to prevent SA overaccumulation. The research also provides strong molecular genetic evidence for an important role of SA in regulating the onset and rate of leaf senescence.
authors: Department of Horticulture, Cornell University, Ithaca, NY 14853, USA.
authors: Kewei
authors: K
authors: Zhang
authors: Rayko
authors: R
authors: Halitschke
authors: Changxi
authors: C
authors: Yin
authors: Chang-Jun
authors: CJ
authors: Liu
authors: Su-Sheng
authors: SS
authors: Gan
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D055162:Biocatalysis; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005841:Gentisates / Q000737:chemistry / Q000378:metabolism; D062385:Hydroxybenzoates / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D013058:Mass Spectrometry; D006899:Mixed Function Oxygenases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D010802:Phylogeny; D018515:Plant Leaves / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism* / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D005841:Gentisates; D062385:Hydroxybenzoates; D012333:RNA, Messenger; C009135:2,3-dihydroxybenzoic acid; D006899:Mixed Function Oxygenases; C584965:salicylic acid 3-hydroxylase, Arabidopsis; D020156:Salicylic Acid; C010925:2,5-dihydroxybenzoic acid
keywords: NahG; aging; benzoic acid; disease resistance; senescence-associated gene
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