Dual control of MAPK activities by AP2C1 and MKP1 MAPK phosphatases regulates defence responses in Arabidopsis.

Mitogen-activated protein kinase (MAPK) cascades transmit environmental signals and induce stress and defence responses in plants. These signalling cascades are negatively controlled by specific Ser/Thr protein phosphatases of the type 2C (PP2C) and dual-specificity phosphatase (DSP) families that inactivate stress-induced MAPKs; however, the interplay between phosphatases of these different types has remained unknown. This work reveals that different Arabidopsis MAPK phosphatases, the PP2C-type AP2C1 and the DSP-type MKP1, exhibit both specific and overlapping functions in plant stress responses.

Targeting alternative splicing by RNAi: from the differential impact on splice variants to triggering artificial pre-mRNA splicing.

Alternative splicing generates multiple transcript and protein isoforms from a single gene and controls transcript intracellular localization and stability by coupling to mRNA export and nonsense-mediated mRNA decay (NMD). RNA interference (RNAi) is a potent mechanism to modulate gene expression. However, its interactions with alternative splicing are poorly understood.

Protein phosphatase AP2C1 negatively regulates basal resistance and defense responses to Pseudomonas syringae.

Mitogen-activated protein kinases (MAPKs) mediate plant immune responses to pathogenic bacteria. However, less is known about the cell autonomous negative regulatory mechanism controlling basal plant immunity. We report the biological role of Arabidopsis thaliana MAPK phosphatase AP2C1 as a negative regulator of plant basal resistance and defense responses to Pseudomonas syringae.

Plant resistance against the parasitic nematode Heterodera schachtii is mediated by MPK3 and MPK6 kinases, which are controlled by the MAPK phosphatase AP2C1 in Arabidopsis.

Plant-parasitic cyst nematodes infect plants and form highly sophisticated feeding sites in roots. It is not known which plant cell signalling mechanisms trigger plant defence during the early stages of nematode parasitism. Mitogen-activated protein kinases (MAPKs) are central components of protein phosphorylation cascades transducing extracellular signals to plant defence responses.

Phosphatases in plants.

Reversible protein phosphorylation is an essential posttranslational modification mechanism executed by opposing actions of protein phosphatases and protein kinases. About 1,000 predicted kinases in Arabidopsis thaliana kinome predominate the number of protein phosphatases, of which there are only ~150 members in Arabidopsis. Protein phosphatases were often referred to as "housekeeping" enzymes, which act to keep eukaryotic systems in balance by counteracting the activity of protein kinases.

Bimolecular fluorescent complementation (BiFC) by MAP kinases and MAPK phosphatases.

The adaptation of plants to the environment is a key property for survival. Adaptation responses to environmental cues are generated in cells by signaling initiated from cell receptors. Signal transduction is based on protein phosphorylation that is employed in mitogen-activated protein kinase (MAPK) cascades to integrate signals from receptors to cellular responses.

Salt-induced subcellular kinase relocation and seedling susceptibility caused by overexpression of Medicago SIMKK in Arabidopsis.

Dual-specificity mitogen-activated protein kinases kinases (MAPKKs) are the immediate upstream activators of MAPKs. They simultaneously phosphorylate the TXY motif within the activation loop of MAPKs, allowing them to interact with and regulate multiple substrates. Often, the activation of MAPKs triggers their nuclear translocation.

The TPLATE adaptor complex drives clathrin-mediated endocytosis in plants.

Clathrin-mediated endocytosis is the major mechanism for eukaryotic plasma membrane-based proteome turn-over. In plants, clathrin-mediated endocytosis is essential for physiology and development, but the identification and organization of the machinery operating this process remains largely obscure. Here, we identified an eight-core-component protein complex, the TPLATE complex, essential for plant growth via its role as major adaptor module for clathrin-mediated endocytosis.

Type 2C protein phosphatases in plants.

Type 2C protein phosphatases (PP2Cs) form a structurally unique class of Mg(2+)-/Mn(2+)-dependent enzymes. PP2Cs are evolutionary conserved from prokaryotes to higher eukaryotes and play a prominent role in stress signalling. In this review, we focus on the evolution, function and regulation of the plant PP2Cs.

Substrate analysis of Arabidopsis PP2C-type protein phosphatases.

Protein phosphorylation by protein kinases can be reversed by the action of protein phosphatases. In plants, the Ser/Thr-specific phosphatases dominate among the protein phosphatase families with the type 2C protein phosphatases (PP2Cs) being the most abundant among them. PP2Cs are monomeric enzymes that require metal cations for their activity and are insensitive to known phosphatase inhibitors.

MAPK phosphatase AP2C3 induces ectopic proliferation of epidermal cells leading to stomata development in Arabidopsis.

In plant post-embryonic epidermis mitogen-activated protein kinase (MAPK) signaling promotes differentiation of pavement cells and inhibits initiation of stomata. Stomata are cells specialized to modulate gas exchange and water loss. Arabidopsis MAPKs MPK3 and MPK6 are at the core of the signaling cascade; however, it is not well understood how the activity of these pleiotropic MAPKs is constrained spatially so that pavement cell differentiation is promoted only outside the stomata lineage.

Phosphatase activities analyzed by in vivo expressions.

Protein phosphatases act to reverse phosphorylation-related modifications induced by protein kinases. Type 2C protein phosphatases (PP2C) are monomeric Ser/Thr phosphatases that require a metal for their activity and are abundant in prokaryotes and eukaryotes. In plants, such as Medicago and Arabidopsis PP2Cs control several essential processes, including ABA signaling, development, and wound-induced mitogen-activated protein kinase (MAPK) pathways.

Regulation of stress hormones jasmonates and ethylene by MAPK pathways in plants.

Plant stress hormones, such as jasmonates (JAs) and ethylene (ET) are essential in plant defence against stress conditions. JAs are used in cosmetics and food flavouring, and the recently demonstrated anti-cancer activity of JAs highlights their potential in health protection. It reinforces the need for a better understanding of biosynthetic regulation of JAs.

Antagonistic regulation of PIN phosphorylation by PP2A and PINOID directs auxin flux.

In plants, cell polarity and tissue patterning are connected by intercellular flow of the phytohormone auxin, whose directional signaling depends on polar subcellular localization of PIN auxin transport proteins. The mechanism of polar targeting of PINs or other cargos in plants is largely unidentified, with the PINOID kinase being the only known molecular component. Here, we identify PP2A phosphatase as an important regulator of PIN apical-basal targeting and auxin distribution.

The PP2C-type phosphatase AP2C1, which negatively regulates MPK4 and MPK6, modulates innate immunity, jasmonic acid, and ethylene levels in Arabidopsis.

Wound signaling pathways in plants are mediated by mitogen-activated protein kinases (MAPKs) and stress hormones, such as ethylene and jasmonates. In Arabidopsis thaliana, the transmission of wound signals by MAPKs has been the subject of detailed investigations; however, the involvement of specific phosphatases in wound signaling is not known. Here, we show that AP2C1, an Arabidopsis Ser/Thr phosphatase of type 2C, is a novel stress signal regulator that inactivates the stress-responsive MAPKs MPK4 and MPK6.

Stress-induced protein phosphatase 2C is a negative regulator of a mitogen-activated protein kinase.

Protein phosphatases of type 2C (PP2Cs) play important roles in eukaryotic signal transduction. In contrast to other eukaryotes, plants such as Arabidopsis have an unusually large group of 69 different PP2C genes. At present, little is known about the functions and substrates of plant PP2Cs.