MYB36 controls differentiation of the endodermis into an ion-selective barrier

Lead Research Organisation: University of Nottingham
Department Name: Sch of Biosciences

Abstract

Roots are the primary organ that acquires the water and mineral nutrients from the soil essential for plant growth and development. A specialized cell layer in the root, called the endodermis, plays a vital role in these processes by regulating entry of water and mineral nutrients into the vascular system of the plant for transport to the shoot. Of critical important to these functions are Casparian strips, structures that form tight seals between cells, blocking nutrients and water leaking between. The only route for nutrients and water into the vascular system is thus through the endodermis. By blocking leakage around cells Casparian strips allow the endodermis to provide cellular control of nutrient and water uptake by roots. Furthermore, to allow the transport of only the nutrients required for growth and development the endodermis contains proteins that allow specific nutrients to be transported directionally across the endodermis from the soil into the vascular system. Despite its importance, the molecular mechanisms involved in how this cell layer becomes specialized to perform these functions are largely unknown. Here, we propose to identify these molecular mechanisms using as a tool the newly discovered MYB36 transcription factor that is know to be involved in controlling the differentiation of the endodermis through regulating the development of Casparian strips.

Technical Summary

The endodermal cell layer in roots acts as a critical checkpoint controlling water and mineral nutrient transport into and out of the root vasculature. To enable this gatekeeping function lignin-based Casparian strips form a transcellular seal between endodermal cells to block uncontrolled extracellular movement of nutrients and water. Construction of Casparian strips requires the deposition of extracellular lignin rings that encircle endodermal cells in the primary cell wall and that are anchored to the plasma membranes of adjacent cells. Many of the molecular details of this process remain to be discovered. Furthermore, to facilitate selective transcellular transport into the vasculature the endodermis contains laterally polarised influx and efflux carriers, though the full extent and function of this set of carriers is unknown. The function of SHORTROOT (SHR) and SCARECROW (SCR) in endodermal specification are well established. However, our understanding of the molecular players that control the programme of differentiation that sets up the endodermis to function as a bidirectional check point for water and mineral nutrient transport remains very limited. This project builds on the PI's recent discovery of the MYB36 transcription factor, a master regulator of Casparian strip formation, published in Proc Natl Acad Sci USA, and highlighted in the same issue with a commissioned commentary. With the discovery of MYB36 the PI now has a new avenue to start investigating the molecular processes involved in endodermal differentiation.

Planned Impact

Results from the proposed research should provide an important molecular mechanistic underpinning to efforts to improve mineral nutrient and water use efficiencies and enhanced stress tolerance (e.g. salinity, flooding, drought, nutrient deficiencies, trace element toxicities) in agricultural and horticultural crops. Commercial farmers could potentially benefit from such developments through improved and sustainable yields with less inputs (fertilizers and water). Further, such improvements in agricultural and horticultural crops could also potentially benefit subsistence farmers with limited access to inorganic fertilizers (primarily nitrogen, phosphate and potassium, secondarily sulphur and magnesium), helping to reduce the cost burden such fertilizers impose. Improved water use efficiency and stress tolerance will also improve yields for subsistence farmers cultivating marginal lands. In addition, reduced utilization of fertilizers, achieved through improved mineral nutrient use efficiencies, will limit the environmental and ecological damage their production and excess use causes, potentially benefiting the general public through enhanced quality of life.

An improved understanding of how roots acquire important trace element and minerals should also provide an important molecular mechanistic underpinning to efforts to improve food quality by helping to increase the content of essential mineral nutrients and reduce toxic trace elements in food crops. For most of the world's population plants are the major source of essential minerals such as calcium, potassium, manganese, iron and zinc, and therefore efforts to improve the mineral nutrient content of staple foods such as rice, maize and cassava will have a positive impact on public health both in the UK and internationally. Plants are also the primary entry point for a variety of toxic minerals into the food chain such as arsenic and cadmium, and being able to limit their accumulation in food would also have a positive impact on public health both in the UK and internationally.

Publications

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Description We have observed that the myb36 sgn3 double mutant completely lacks endodermal lignification and has no apoplastic barrier along the full length of the root. This is unique. Further, this double mutant has low fitness and has an extreme leaf ionome. Uisng this double mutant we also have evidence that MYB36 regulates expression of genes encoding proteins involved in the tight attachment of the plasma membrane to the Casparian strip. We have also now completed the development of the various cell-type specific marker lines and mutant combinations required to test the role of Casparian strips in radial ion transport and endodermal development.
Exploitation Route The complete lack of an apoplastic barrier in myb36 sgn3 provides an excellent system for studying the physiological role of this barrier in plants.
Sectors Agriculture, Food and Drink,Environment

 
Description ERA-CAPS Root Barriers 
Organisation INRA (UMR-MISTEA) Montpellier, France
Country France 
Sector Academic/University 
PI Contribution Molecular plant physiology including Casparian strip development
Collaborator Contribution David E Salt (project leaders) at the University of Aberdeen is the overall coordinator for the consortium. The work of the consortium is split into five main work packages being performed at six institutions by eight groups. Work packages 1 and 2 at Aberdeen and Bonn will deliver a molecular mechanistic understanding of the genes and biochemical processes involved in the biosynthesis of Casparian strips and suberin. Mutant resources developed in work package 1 and 2 will be provided to labs performing work packages 3, 4 and 5 at the IPK, Copenhagen, Wageningen, INRA and Bonn, in order to develop a fuller understanding of physiological roles of the Casparian strip and suberin barriers.
Impact Held the first partnership meeting in Aberdeen in May 2014 to start the project. Each group has hired a postdoc or grad student as part of the project. A core set of A. thaliana mutants has been established and shared with each group.
Start Year 2014
 
Description ERA-CAPS Root Barriers 
Organisation Leibniz Association
Department Leibniz Institute of Plant Genetics and Crop Plant Research
Country Germany 
Sector Charity/Non Profit 
PI Contribution Molecular plant physiology including Casparian strip development
Collaborator Contribution David E Salt (project leaders) at the University of Aberdeen is the overall coordinator for the consortium. The work of the consortium is split into five main work packages being performed at six institutions by eight groups. Work packages 1 and 2 at Aberdeen and Bonn will deliver a molecular mechanistic understanding of the genes and biochemical processes involved in the biosynthesis of Casparian strips and suberin. Mutant resources developed in work package 1 and 2 will be provided to labs performing work packages 3, 4 and 5 at the IPK, Copenhagen, Wageningen, INRA and Bonn, in order to develop a fuller understanding of physiological roles of the Casparian strip and suberin barriers.
Impact Held the first partnership meeting in Aberdeen in May 2014 to start the project. Each group has hired a postdoc or grad student as part of the project. A core set of A. thaliana mutants has been established and shared with each group.
Start Year 2014
 
Description ERA-CAPS Root Barriers 
Organisation University of Bonn
Country Germany 
Sector Academic/University 
PI Contribution Molecular plant physiology including Casparian strip development
Collaborator Contribution David E Salt (project leaders) at the University of Aberdeen is the overall coordinator for the consortium. The work of the consortium is split into five main work packages being performed at six institutions by eight groups. Work packages 1 and 2 at Aberdeen and Bonn will deliver a molecular mechanistic understanding of the genes and biochemical processes involved in the biosynthesis of Casparian strips and suberin. Mutant resources developed in work package 1 and 2 will be provided to labs performing work packages 3, 4 and 5 at the IPK, Copenhagen, Wageningen, INRA and Bonn, in order to develop a fuller understanding of physiological roles of the Casparian strip and suberin barriers.
Impact Held the first partnership meeting in Aberdeen in May 2014 to start the project. Each group has hired a postdoc or grad student as part of the project. A core set of A. thaliana mutants has been established and shared with each group.
Start Year 2014
 
Description ERA-CAPS Root Barriers 
Organisation University of Copenhagen
Country Denmark 
Sector Academic/University 
PI Contribution Molecular plant physiology including Casparian strip development
Collaborator Contribution David E Salt (project leaders) at the University of Aberdeen is the overall coordinator for the consortium. The work of the consortium is split into five main work packages being performed at six institutions by eight groups. Work packages 1 and 2 at Aberdeen and Bonn will deliver a molecular mechanistic understanding of the genes and biochemical processes involved in the biosynthesis of Casparian strips and suberin. Mutant resources developed in work package 1 and 2 will be provided to labs performing work packages 3, 4 and 5 at the IPK, Copenhagen, Wageningen, INRA and Bonn, in order to develop a fuller understanding of physiological roles of the Casparian strip and suberin barriers.
Impact Held the first partnership meeting in Aberdeen in May 2014 to start the project. Each group has hired a postdoc or grad student as part of the project. A core set of A. thaliana mutants has been established and shared with each group.
Start Year 2014
 
Description ERA-CAPS Root Barriers 
Organisation University of Wageningen
Country Netherlands 
Sector Academic/University 
PI Contribution Molecular plant physiology including Casparian strip development
Collaborator Contribution David E Salt (project leaders) at the University of Aberdeen is the overall coordinator for the consortium. The work of the consortium is split into five main work packages being performed at six institutions by eight groups. Work packages 1 and 2 at Aberdeen and Bonn will deliver a molecular mechanistic understanding of the genes and biochemical processes involved in the biosynthesis of Casparian strips and suberin. Mutant resources developed in work package 1 and 2 will be provided to labs performing work packages 3, 4 and 5 at the IPK, Copenhagen, Wageningen, INRA and Bonn, in order to develop a fuller understanding of physiological roles of the Casparian strip and suberin barriers.
Impact Held the first partnership meeting in Aberdeen in May 2014 to start the project. Each group has hired a postdoc or grad student as part of the project. A core set of A. thaliana mutants has been established and shared with each group.
Start Year 2014
 
Description Niko Geldner Université de Lausanne 
Organisation University of Lausanne
Department Department of Plant Molecular Biology
Country Switzerland 
Sector Academic/University 
PI Contribution The Salt group works very closely with the group of Niko Geldner on the molecular biology and function of root diffusional barriers at the endodermis, including Casparian strips and suberin. We share reagents and analytical expertise in ICP-MS and mineral nutrient homeostasis.
Collaborator Contribution The group of Niko Geldner shares reagents, protocols and expertise in cell biology including confocal microscopy.
Impact 1: Li B, Kamiya T, Kalmbach L, Yamagami M, Yamaguchi K, Shigenobu S, Sawa S, Danku JM, Salt DE, Geldner N, Fujiwara T. Role of LOTR1 in Nutrient Transport through Organization of Spatial Distribution of Root Endodermal Barriers. Curr Biol. 2017 Mar 6;27(5):758-765. doi: 10.1016/j.cub.2017.01.030. PubMed PMID: 28238658. 2: Barberon M, Vermeer JE, De Bellis D, Wang P, Naseer S, Andersen TG, Humbel BM, Nawrath C, Takano J, Salt DE, Geldner N. Adaptation of Root Function by Nutrient-Induced Plasticity of Endodermal Differentiation. Cell. 2016 Jan 28;164(3):447-59. doi: 10.1016/j.cell.2015.12.021. PubMed PMID: 26777403. 3: Kamiya T, Borghi M, Wang P, Danku JM, Kalmbach L, Hosmani PS, Naseer S, Fujiwara T, Geldner N, Salt DE. The MYB36 transcription factor orchestrates Casparian strip formation. Proc Natl Acad Sci U S A. 2015 Aug 18;112(33):10533-8. doi: 10.1073/pnas.1507691112. PubMed PMID: 26124109; PubMed Central PMCID: PMC4547244. 4: Geldner N, Salt DE. Focus on roots. Plant Physiol. 2014 Oct;166(2):453-4. doi: 10.1104/pp.114.900494. PubMed PMID: 25288635; PubMed Central PMCID: PMC4213078. 5: Pfister A, Barberon M, Alassimone J, Kalmbach L, Lee Y, Vermeer JE, Yamazaki M, Li G, Maurel C, Takano J, Kamiya T, Salt DE, Roppolo D, Geldner N. A receptor-like kinase mutant with absent endodermal diffusion barrier displays selective nutrient homeostasis defects. Elife. 2014 Sep 16;3:e03115. doi: 10.7554/eLife.03115. PubMed PMID: 25233277; PubMed Central PMCID: PMC4164916. 6: Hosmani PS, Kamiya T, Danku J, Naseer S, Geldner N, Guerinot ML, Salt DE. Dirigent domain-containing protein is part of the machinery required for formation of the lignin-based Casparian strip in the root. Proc Natl Acad Sci U S A. 2013 Aug 27;110(35):14498-503. doi: 10.1073/pnas.1308412110. Erratum in: Proc Natl Acad Sci U S A. 2013 Oct 1;110(40):16283. PubMed PMID: 23940370; PubMed Central PMCID: PMC3761638.
Start Year 2011
 
Description 2nd Workshop on Plant Development & Drought Stress, Asilomar, Pacific Grove, USA 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Give a talk on role of Casparian strip on water and ion transport at the 2nd Workshop on Plant Development & Drought Stress, Asilomar, Pacific Grove, USA
Year(s) Of Engagement Activity 2017
 
Description Casparian strip as a transport gateway, IPNC, Copenhagen 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Gave a talk on the Casparian strip as a transport gateway, IPNC, Copenhagen
Year(s) Of Engagement Activity 2017
 
Description Keynote lecture, 2nd Asia-Pacific Plant Phenotyping Conference, Nanjing, China 23 - 25th March, 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Key note talk on ionomic phenotyping
Year(s) Of Engagement Activity 2018
 
Description Max Planck Institute of Plant Breeding Research, Cologne, Germany, 24th Oct, 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk at the Max Planck Institute for Plant Breeding
Year(s) Of Engagement Activity 2018
 
Description Pennsylvania State University, Department of Plant Sciences, State College, USA, 11th Oct, 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk at Penn State Plant Science Department
Year(s) Of Engagement Activity 2018
 
Description School of Biological Sciences, University of Birmingham, UK 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Give a talk on Casparian strip biogenesis at School of Biological Sciences, University of Birmingham, UK
Year(s) Of Engagement Activity 2018
 
Description University of Lausanne, Lausanne, Switzerland, 14th Feb, 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk at the Department of Plant Molecular Biology, University of Lausanne
Year(s) Of Engagement Activity 2019