Phosphorylation of 1-Aminocyclopropane-1-Carboxylic Acid Synthase by MPK6, a Stress-Responsive Mitogen-Activated Protein Kinase, Induces Ethylene Biosynthesis in Arabidopsis[W]

Abstract

Mitogen-activated protein kinases (MAPKs) are implicated in regulating plant growth, development, and response to the environment. However, the underlying mechanisms are unknown because of the lack of information about their substrates. Using a conditional gain-of-function transgenic system, we demonstrated that the activation of SIPK, a tobacco (Nicotiana tabacum) stress-responsive MAPK, induces the biosynthesis of ethylene. Here, we report that MPK6, the Arabidopsis thaliana ortholog of tobacco SIPK, is required for ethylene induction in this transgenic system. Furthermore, we found that selected isoforms of 1-aminocyclopropane-1-carboxylic acid synthase (ACS), the rate-limiting enzyme of ethylene biosynthesis, are substrates of MPK6. Phosphorylation of ACS2 and ACS6 by MPK6 leads to the accumulation of ACS protein and, thus, elevated levels of cellular ACS activity and ethylene production. Expression of ACS6 DDD , a gain-of-function ACS6 mutant that mimics the phosphorylated form of ACS6, confers constitutive ethylene production and ethylene-induced phenotypes. Increasing numbers of stress stimuli have been shown to activate Arabidopsis MPK6 or its orthologs in other plant species. The identification of the first plant MAPK substrate in this report reveals one mechanism by which MPK6/ SIPK regulates plant stress responses. Equally important, this study uncovers a signaling pathway that modulates the biosynthesis of ethylene, an important plant hormone, in plants under stress.

Activation of Ntf4, a Tobacco Mitogen-Activated Protein Kinase, during Plant Defense Response and Its Involvement in Hypersensitive Response-Like Cell Death

“…SIPK was implicated in signaling various plant defense responses. One specific role of SIPK is to regulate the ethylene production in plants under stress Liu and Zhang, 2004). SIPK was shown to be expressed in at least leaf tissues and suspension-cultured To facilitate the detection of transgene expression, a Flag tag was added to the N terminus of Ntf4.…”

“…Ntf4 and its mutants with a Flag epitope at their N termini were inserted into the XhoI-SpeI sites of the steroid-inducible pTA7002 binary vector (Aoyama and Chua, 1997) or a modified pBI121 binary vector for constitutive expression as described previously Liu and Zhang, 2004). Four-or 6-week-old tobacco plants were used for experiments.…”

Pseudomonas syringae type III effector HopAF1 suppresses plant immunity by targeting methionine recycling to block ethylene induction

“…Recognition of flg22 triggers the activation of a MAPK cascade that leads to an increase in ethylene biosynthesis (7)(8)(9). The type III secretion system-deficient mutant Pto DC3000 hrcC triggers more ethylene biosynthesis than wild-type Pto DC3000 (Fig.…”

A Comparison of Two Nicotiana attenuata Accessions Reveals Large Differences in Signaling Induced by Oral Secretions of the Specialist Herbivore Manduca sexta

“…Activation of SIPK and WIPK, upstream signal transduction components that modulate downstream phytohormonal and transcriptional changes in plants, is crucial for plants' ability to initiate herbivore resistance (Zhang and Klessig, 2001;Liu and Zhang, 2004;Wu et al, 2007a).…”