Editors' ChoicePlant biology

First Plant MAP Kinase Substrate

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Science's STKE  14 Dec 2004:
Vol. 2004, Issue 263, pp. tw447
DOI: 10.1126/stke.2632004tw447

The Arabidopsis mitogen-activated protein kinase (MAPK) MPK6 has been proposed to participate in signaling through the ethylene receptor. New evidence from Liu and Zhang now suggests that MPK6 does not respond to ethylene signals. Rather, it appears to be a key regulator of synthesis of the gaseous plant hormone ethylene. Ethylene is produced in response to a broad range of stress signals in the plant, and MPK6 appears to be a key regulator of this response. Activation of MPK6 through expression of an exogenous MAPK showed that MPK6 promotes the synthesis of ethylene in a manner that depends on activation of ACS (1-aminocyclopropane-1-carboxylic acid synthase), which catalyzes the rate-limiting step in ethylene biosynthesis. In vitro studies showed that ACS isoforms are direct substrates of MPK6. Furthermore, phosphorylation of ACS in response to wounding was lost in mpk6 knockout plants. Protein immunoblotting showed that phosphorylation of ACS was associated with increased stability (and thus increased abundance) of the protein. Ecker provides commentary on the findings and helps reconcile them with previous contradictory results in the literature.

Y. Liu, S. Zhang, Phosphorylation of 1-aminocyclopropane-1-carboxylic acid synthase by MPK6, a stress-responsive mitogen-activated protein kinase, induces ethylene biosynthesis in Arabidopsis. Plant Cell 16, 3386-3399 (2004). [Abstract] [Full Text]

J. R. Ecker, Reentry of the ethylene MPK6 module. Plant Cell 16, 3169-3173 (2004). [Full Text]