MAPK-mediated regulation of the bHLH SPEECHLESS and stomatal initiation

 

Arabidopsis stomatal initiation is controlled by MAPK-mediated regulation of the bHLH SPEECHLESS.

by Lampard G. R., MacAlister C. A., Bergmann D. C. (2008)

Gregory R. Lampard

Cora A. MacAlister

Dominique C. Bergmann

in Science 322:1113–1116. – 10.1126/science.1162263.-

Abstract/FREE Full Text– View Article, PubMed – PubMed Abstract | CrossRef Full Text | Google Scholar 

http://science.sciencemag.org/content/322/5904/1113?ijkey=df714adae2744d85ba31cc45b355bced9ca8238b&keytype2=tf_ipsecsha

Fig. 4. Effects of endogenous stomatal regulators on SPCH function. (A) Scheme of known stomatal regulatory pathway (P, phosphorylation). (B to D) Suppression of tmm-1–mediated enhancement of SPCHpro::SPCH phenotypes by CA-YODA. (B) Baseline of tmm-1 clustered stomata. (C) Enhanced clusters in SPCHpro::SPCH; tmm-1. (D) Block in excess stomatal production by CA-YODA in SPCHpro::SPCH; tmm-1. (E to G) Enhancement of SPCH activity in erl1;erl2 mutant background. (E) erl1;erl2 with no stomatal clusters, (F) SPCHpro::SPCH; erl1;erl2, and (G) SPCHpro::SPCHΔ49; erl1;erl2 all result in a statistically significant increase in the stomatal density and fraction of stomata in clusters. (H to J) Lack of enhancement of SPCH by sdd1. (H) sdd1 mutants exhibit pairing of stomata and increased density. Expression of SPCHpro::SPCH (I) or SPCHpro::SPCHΔ49 (J) in sdd1 does not enhance the sdd1 stomatal overproduction phenotype. – https://d2ufo47lrtsv5s.cloudfront.net/content/sci/322/5904/1113/F4.medium.gif

Abstract

Stomata, epidermal structures that modulate gas exchange between plants and the atmosphere, play critical roles in primary productivity and the global climate. Positively acting transcription factors and negatively acting mitogen-activated protein kinase (MAPK) signaling control stomatal development in Arabidopsis; however, it is not known how the opposing activities of these regulators are integrated.

We found that a unique domain in a basic helix-loop-helix (bHLH) stomatal initiating factor, SPEECHLESS, renders it a MAPK phosphorylation target in vitro and modulates its function in vivo.

MAPK cascades modulate a diverse set of activities including development, cell proliferation, and response to external stresses. The coupling of MAPK signaling to SPEECHLESS activity provides cell type specificity for MAPK output while allowing the integration of multiple developmental and environmental signals into the production and spacing of stomata.

See also : Sharghi K. (2008) – Stanford researchers investigate how plants adapt to climate – https://news.stanford.edu/news/2008/december3/stomata-120308.html –

How many mouths does a plant need in order to survive? The answer changes depending on climate, and some of the decisions are made long before a new leaf sprouts.

Stanford researchers have found that the formation of microscopic pores called stomata (derived from the Greek word stoma, meaning mouth) is controlled by a specific signaling pathway that blocks activity of a single protein required for stomata development. The findings are described in a paper published Nov. 14 in Science.

Stomata are found on almost every terrestrial plant on Earth. Their multiple roles include releasing moisture and oxygen into the environment, providing internal air conditioning for the plant and allowing carbon dioxide to enter the leaf, where it is converted to sugar during photosynthesis. Stomata are essential for the survival of plants and, by absorbing carbon from the atmosphere, play a significant role in maintaining the health of the planet.

Using Arabidopsis thaliana, a fast-growing, flowering plant used for genetic and developmental studies, Dominique Bergmann, an assistant professor of biology, and paper co-authors Gregory Lampard, a postdoctoral fellow, and Cora MacAlister, a PhD student, found a unique structural region on a protein with 10 sites that can be modified by a well-known, environmentally-controlled signaling pathway to dictate the number of stomata a plant makes.

“Scientists have said that the environment affects plant development, but no one could point to a protein that was responsible for that response,” Bergmann said. “Now we know a major target inside the cell and how it is regulated.”

MAPK signaling in Arabidopsis stomata

 

Novel and expanded roles for MAPK signaling in Arabidopsis stomatal cell fate revealed by cell type-specific manipulations

by Lampard G. R., Lukowitz W., Ellis B. E., Bergmann D. C. (2009)

in Plant Cell 2009,21:3506-3517.

(PubMed Abstract | Publisher Full Text|PubMed Central Full Text) – 

PMID: 19897669 

http://www.plantcell.org/content/21/11/3506/F1.medium.gif

Figure 1.

Diagram of Stomatal Lineage Development and Gene Expression Patterns.

Arabidopsis stomatal development follows a three-step stereotyped pathway that involves a series of asymmetric and symmetric cell divisions. Entry into the stomatal lineage is negatively regulated by a MAPK module containing YDA (MAPKKK), MKK4 and MKK5 (MAPKKs), and MPK3 and MPK6 (MAPKs). Progression through the developmental pathway is positively influenced by sequentially acting bHLH transcription factors, SPCH, MUTE, and FAMA, which regulate entry (1), progression through (2), and terminal differentiation of guard cell development (3), respectively. The expression of green fluorescent protein (GFP)-tagged transcriptional reporters of each of SPCH (A), MUTE (B), andFAMA (C) coincides with each major developmental transition. Bars = 50 μm.

Abstract

Mitogen-activated protein kinase (MAPK) signaling networks regulate numerous eukaryotic biological processes. In Arabidopsis thaliana, signaling networks that contain MAPK kinases MKK4/5 and MAPKs MPK3/6 function in abiotic and biotic stress responses and regulate embryonic and stomatal development.

However, how single MAPK modules direct specific output signals without cross-activating additional downstream processes is largely unknown.

Studying relationships between MAPK components and downstream signaling outcomes is difficult because broad experimental manipulation of these networks is often lethal or associated with multiple phenotypes.

Stomatal development in Arabidopsis follows a series of discrete, stereotyped divisions and cell state transitions. By expressing a panel of constitutively active MAPK kinase (MAPKK) variants in discrete stomatal lineage cell types, we identified a new inhibitory function of MKK4 and MKK5 in meristemoid self-renewal divisions.

Furthermore, we established roles for MKK7 and MKK9 as both negative and (unexpectedly) positive regulators during the major stages of stomatal development. This has expanded the number of known MAPKKs that regulate stomatal development and allowed us to build plausible and testable subnetworks of signals. This in vivo cell type-specific assay can be adapted to study other protein families and thus may reveal insights into other complex signal transduction pathways in plants.

See the text: NCBI

Read the full article: The Plant Cell

Structural domains of four “stomatal” MKKs in stomatal development

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4371834/bin/pc_127415_f5.jpg

The D-Domains of MKK7/9 Are Not Absolutely Necessary for CAMKK7/9 Functions in Stomatal Development.

(A) Protein schematic (left) and images of phenotypes associated with expressing CAMKK7 in the SPCH, MUTE, and FAMA stages of stomatal development as indicated.

(B) and (C) The cotyledon epidermis of plants expressing CAMKK7ΔD in the SPCH (B) and MUTE (C) stages generally have wild-type stomatal distribution.

(D) and (E) The cotyledon epidermis of plants expressing CAMKK7ΔD in the FAMA stage. The majority of these plants have wild-type stomatal development but occasionally have limited clusters of stomata.

(F) to (I) Cotyledon epidermis of plants expressing CAMKK9ΔD plants in the SPCH (F), MUTE (G), and FAMA ([H] and [I]) stages. CAMKK9ΔD has impacts on stomatal development in the same fashion as CAMKK7ΔD.

The relative activity of each kinase variant in in vitro kinase assays is depicted as follows (+, less active than full length; ++, comparable activity to the full-length CAMKK). Hashed boxes in schematic representations of kinase variants indicate the region(s) that were removed. All images are of 10-DPG abaxial cotyledons, and bars = 25 μm.

Manipulation of Mitogen-Activated Protein Kinase Kinase Signaling in the Arabidopsis Stomatal Lineage Reveals Motifs That Contribute to Protein Localization and Signaling Specificity

by Lampard G. R., Wengier D. L., Bergmann D. C. (2014)

in Plant Cell 2014 Aug; pii: tpc.114.127415. [Epub ahead of print] –

PMID: 25172143 – 

http://www.ncbi.nlm.nih.gov/pubmed/?term=25172143 

Abstract

When multiple mitogen-activated protein kinase (MAPK) components are recruited recurrently to transduce signals of different origins, and often opposing outcomes, mechanisms to enforce signaling specificity are of utmost importance. These mechanisms are largely uncharacterized in plant MAPK signaling networks.

The Arabidopsis thaliana stomatal lineage was previously used to show that when rendered constitutively active, four MAPK kinases (MKKs), MKK4/5/7/9, are capable of perturbing stomatal development and that these kinases comprise two pairs, MKK4/5 and MKK7/9, with both overlapping and divergent functions.

We characterized the contributions of specific structural domains of these four “stomatal” MKKs to MAPK signaling output and specificity both in vitro and in vivo within the three discrete cell types of the stomatal lineage.

These results verify the influence of functional docking (D) domains of MKKs on MAPK signal output and identify novel regulatory functions for previously uncharacterized structures within the N termini of MKK4/5. Beyond this, we present a novel function of the D-domains of MKK7/9 in regulating the subcellular localization of these kinases.

These results provide tools to broadly assess the extent to which these and additional motifs within MKKs function to regulate MAPK signal output throughout the plant.

See the text: NCBI