Relationship between ethylene and auxin signalling in Arabidopsis root development

Lead Research Organisation: Durham University
Department Name: Biological and Biomedical Sciences

Abstract

The growth and development of plants is controlled by a combination of genetic programming and environmental influence. For example, the patterning of floral organs is altered very little by the environment, and can be considered to be strongly dependent on genetic factors; but other aspects of plant development, such as the timing of flowering or the growth or leaves or roots, is much more dependent on prevailing conditions of temperature, water and nutrient availability, and so on. The effects of environment on gene expression and developmental changes are coordinated by plant hormones. One such hormone, the gas ethylene, influences many developmental processes, including root growth and development. The aim of this grant is to understand better how it interacts with another key hormone, auxin, to control gene expression and cellular organization in the root. We have already found that one particular mutant of the plant Arabidopsis, the polaris mutant, is unable to regulate correctly its ethylene responses, resulting in a shortened root system typical of plants that have been over-exposed to ethylene. At the same time, this ethylene problem affects the transport and accumulation of auxin in the root, previously found to be important in regulating root development. We hope to understand better the link between ethylene, auxin and root growth, by studying different ethylene mutants for altered auxin transport and accumulation, cellular organization and root growth.

Technical Summary

We have found that the POLARIS (PLS) gene, encoding a 36 amino acids peptide, is required for correct ethylene and auxin signalling, and for Arabidopsis root development. The pls mutant exhibits developmental abnormalities, and in particular a short root phenotype. A key discovery has been that pls seedlings exhibit a triple response phenotype when grown in air in the dark, similar to the ethylene signalling mutant ctr1 or to ethylene overproducers, such as eto1 or eto2. The pls mutant does not overproduce ethylene, strongly suggesting that the PLS gene is required for regulation of ethylene signalling. Significantly, overexpression of the PLS peptide-encoding region of the PLS cDNA completely suppresses the triple response phenotype. The mutant also shows dramatically reduced auxin transport and accumulation of free IAA. These auxin defects and the root defects are largely rescued by the inhibition of ethylene signalling, either genetically or pharmacologically. These results indicate that PLS is a negative regulator of ethylene signalling, and is a novel example of a peptide as a modulator of hormone signalling in plants. We now also have strong evidence that ethylene defects in the pls mutant affect microtubule dynamics, and a failure of correct PIN2 recycling. We hypothesize that PLS is a component of the system regulting ethylene signalling, to modulate auxin transport via cytoskeleton dynamics and PIN localization. We also hypothesize that correct ethylene signalling is required for the expression of auxin-regulated genes such as PLS, IAA2 and PLT, to permit root meristem function and cellular patterning. We aim to test these hypotheses further, by investigating auxin transport, PIN recycling, cytoskeleton dynamics and gene expression in a range of ethylene mutants other than pls.
 
Description We have identified and characterised genes involved in regulating the complex interactions between hormone signalling pathways that affect root development in plants. We constructed the first predictive mathematical model to help us understand better these interactions in the root. This is important for future understanding of the mechanisms by which roots response to environmental stresses, including drought, nutrient stress and attack by pathogens such as plant-parasitic nematodes.
Exploitation Route We have developed new understanding of the genetics of root development; have constructed new mathematical models that have been of use to other labs; and have worked with industry to understand better the response of roots of crops to nutritional stress and effects of fertilisers.
Sectors Agriculture, Food and Drink,Chemicals,Education,Environment

 
Description Our results have led to new understanding of cross-talk between hormone signalling pathways, and have led to new projects on developing predictive mathematical models to describe the complexity of these networks. We also have new projects building on experimental aspects of the work, which provide new insights into gene-signalling networks in root development in plants, including plant responses to drought and nutrient stress.
First Year Of Impact 2006
Sector Agriculture, Food and Drink,Education
 
Title Gene-hormone network modelling 
Description We have generated the first predictive model of a plant gene-hormone signalling network. 
Type Of Material Computer model/algorithm 
Year Produced 2010 
Provided To Others? Yes  
Impact Other labs are now developing mathematical models that use our general approach. 
 
Description Modelling plant development 
Organisation University of Ghent
Country Belgium 
Sector Academic/University 
PI Contribution Mathematical modelling of gene-hormone signalling interactions in root development.
Collaborator Contribution PIN protein localisation and analysis.
Impact Research papers
 
Description Plant-parasitic nematode interactions 
Organisation University of Castile-La Mancha
Country Spain 
Sector Academic/University 
PI Contribution We have provided expertise in laser-capture micro dissection, which we have applied to the analysis in gene expression changes in plant roots following infection with plant-parasitic nematodes.
Collaborator Contribution They have provided expertise in nematology.
Impact Research papers, basis for spin-out company activities. Multidisciplinary: plant molecular biology, plant development, nematology
 
Description Plant-parasitic nematode interactions 
Organisation University of Ghent
Country Belgium 
Sector Academic/University 
PI Contribution Expertise in plant genetic, gene tagging, laser-capture micro dissection.
Collaborator Contribution Nematology
Impact Research papers.
 
Description Root growth 
Organisation Sirius plc
Country United Kingdom 
Sector Private 
PI Contribution Plant development, growth measurements
Collaborator Contribution Provision of novel fertiliser, equipment
Impact Novel information on the effects of potash on plant development. Contribution to the company's business plan. Multidisciplinarity: plant development, geology
Start Year 2012
 
Title Improvements in or relating to control of gene expression in plants. 
Description Development of a gene promoter for plant resistance to nematodes. 
IP Reference WO2006097685 
Protection Patent application published
Year Protection Granted 2006
Licensed Commercial In Confidence
Impact Supported the development of a son-out company.
 
Company Name Creative Gene Technology Ltd. 
Description Generation of IP around plant agritech business, with interests in plant protection and plant yield. 
Impact Employment of staff in a region of the UK with high unemployment.