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Salicylic acid 3-hydroxylase regulates Arabidopsis leaf longevity by mediating salicylic acid catabolism

Kewei Zhang, Rayko Halitschke, Changxi Yin, Chang-Jun Liu and Su-Sheng Gan
Proceedings of the National Academy of Sciences of the United States of America
Vol. 110, No. 36 (September 3, 2013), pp. 14807-14812
Stable URL: http://www.jstor.org/stable/42713195
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Salicylic acid 3-hydroxylase regulates Arabidopsis leaf
                            longevity by mediating salicylic acid catabolism
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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. 53H 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.

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