Regulation of Auxin Fluxes Required for Phototropic Growth

Lead Research Organisation: University of Glasgow
Department Name: College of Medical, Veterinary &Life Sci

Abstract

Plants depend on sunlight for photosynthesis and adapt their growth to optimise light capture. Phototropism, the reorientation of growth towards light, represents one of these important adaptive responses. Modern-day studies of phototropism began with experiments in monocotyledonous grasses by Charles Darwin and led ultimately to the discovery of the plant growth hormone auxin, establishing the concept that light perception at the shoot apex triggers differential bending in the tissues below. In the past two decades, molecular-genetic analysis in the model flowering plant Arabidopsis thaliana has identified the principle photoreceptor for phototropism, phot1, as well as the major auxin transporters. Despite extensive efforts, however, how the photoreceptor regulates auxin transport so as to establish differential growth is poorly understood, as is whether this process is conserved between monocots and dicots. Therefore, the key aim of this proposal is to identify and characterise the signalling events associated with establishing auxin fluxes required for phototropic growth. By adopting a revised approach to study phototropism in Arabidopsis in the absence of developmental events that are typically associated with seedling photomorphogenesis, we have shown that the proximity of light perception and differential growth is conserved between monocots and dicots: in both plant types, differential growth is a consequence of lateral auxin movements across the shoot apex. Moreover, we have identified two auxin transporter proteins, PIN-FORMED (PIN3) and ATP-BINDING CASSETTE B19 (ABCB19), that contribute to these movements, the latter of which is directly regulated by phot1 and serves to prime lateral auxin fluxes in the shoot apex. These findings uncover new mechanistic information of the events coupling photoreception and auxin signalling, two processes that are critical for shaping plant growth. Hence, this proposal is focused on further characterising the molecular processes involved in establishing phototropic growth. Given the fundamental importance of both light and auxin in controlling plant development, these insights should ultimately provide new strategies to manipulate plant growth for agronomic gain.

Technical Summary

It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. We have established a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. By doing so, we have found that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we have identified the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these findings provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperms. The experiments outlined in this proposal are therefore aimed at further understanding how phot1 regulates auxin transport through ABCB19 and PIN3. In addition, cell biological and proteomic strategies will be employed to identify the role of additional targets of phot1 action that contribute to auxin movements required for phototropism in dicots and monocots. Together, this work will provide significant advances in our mechanistic understanding of how light and auxin signals are coordinated to shape the developmental plasticity of plants.

Planned Impact

Beneficiaries
Beneficiaries of the research include: academic scientists interested in the effects of light and hormone signalling on plant development, synthetic biologists interested in the design of artificial photoreceptor systems, commercial organisations interested in developing new strategies to improve crop production, companies interested in the design of specialised light facilities for the growth of glasshouse crops, individuals (text books for teaching), and organisations involved in science communication to schools and to the wider public (e.g. Glasgow Science Centre). Phototropism research will also benefit the general public who can relate to the work of Charles Darwin and its impact on science and evolution.

Benefits
The impact of the research is derived from its relevance to understanding how light and hormone signalling is co-coordinately regulated to control plant growth, as well as its potential relevance to crop improvement for agronomic gain. Light and auxin are both critical for plant growth and development. Light signalling mediated by phototropin blue light receptors is of significant importance, as they function to regulate numerous adaptive responses (e.g. phototropism, solar tracking, leaf expansion, chloroplast positioning, regulation of water loss) that serve to optimise photosynthetic efficiency to promote growth. Phototropism, for instance, imparts adaptive significance under field conditions and enhances fitness under drought through increases in root growth efficiency close to the soil surface. Thus, research on phototropin function has potential to generate novel strategies to increase the efficiency of photosynthesis that will potentially provide solutions for the food, energy, and environmental challenges of the future. Phototropin signalling pathways are also known to prime plant defence responses and potentiate pathogen resistance. In addition, functional knowledge of phototropin function will facilitate advances in synthetic biology aimed at regulating enzymatic activities by light. Understanding how phototropins regulate auxin transport is also highly relevant to manipulating plant stature, a major objective in the production of agricultural and horticultural crops. For many species, height control is essential to optimise their establishment and promote efficient handling. Reduced levels of the auxin transporter ABCB19 causes dwarfing in maize and sorgham and, as a consequence, improves crop yield. A greater understanding of auxin transport regulation therefore has considerable potential to create new avenues for crop improvement that could benefit farmers, consumers and the environment and contribute to the economic competitiveness of the UK. Such studies will also have impacts on medical research. Related proteins in humans are responsible for drug resistance in tumours. Understanding ABCB function in plants and how these proteins are regulated biochemically could therefore have implications for drug resistance, cancer research and human health. The staff assigned to the project will obtain knowledge and expertise that can be applied in related research fields or more widely in the commercial or public sectors.

Activities
The proposed project will be continually managed by the PI to engage potential beneficiaries. The PI will publish the research in high-impact scientific journals, write reviews and book chapters and inform the University Media Relations Office of research highlights. Discussions with relevant commercial organisations will be initiated when appropriate to promote exploitation. The PI will communicate the research to school and university students via visits and University open days, initiate discussions with the Glasgow Science Centre, and present lectures at national and international conferences, as well as within Universities throughout the UK. The PI's web site will be routinely updated to communicate the research to the general public.

Publications

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Buckley AM (2015) LOV-based reporters for fluorescence imaging. in Current opinion in chemical biology

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Christie JM (2013) Shoot phototropism in higher plants: new light through old concepts. in American journal of botany

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Christie JM (2015) Plant flavoprotein photoreceptors. in Plant & cell physiology

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Cosentino C (2015) Optogenetics. Engineering of a light-gated potassium channel. in Science (New York, N.Y.)

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Fankhauser C (2015) Plant phototropic growth. in Current biology : CB

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Petersen J (2017) Functional characterization of a constitutively active kinase variant of phototropin 1. in The Journal of biological chemistry

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Schnabel J (2018) A chemical genetic approach to engineer phototropin kinases for substrate labeling. in The Journal of biological chemistry

 
Description We have uncovered new information on the molecular mechanisms controlling plant phototropism that has resulted in publication of several research papers and reviews.
Exploitation Route Tools and materials have been developed during the course of the research that will support further projects and have been disseminated to laboratories worldwide.
Sectors Agriculture, Food and Drink

 
Description In connection with a PhD student placement: http://www.gla.ac.uk/colleges/mvls/graduateschool/bbsrcwestbiodtp/pipscasestudies/#/growingcommunicationskills
First Year Of Impact 2013
Sector Agriculture, Food and Drink
Impact Types Societal

 
Title BLINK1 
Description Light regulated potassium channel that has potential in neural silencing. Now demonstrated utility in plants (Science paper pending). Patent has been filed in collaboration with PBL. 
Type Of Material Technology assay or reagent 
Year Produced 2015 
Provided To Others? Yes  
Impact Published in Science and awaiting further examination of its utility for optogenetics. 
 
Description Auxin 
Organisation University of Maryland
Country United States 
Sector Academic/University 
PI Contribution Collaborations made between Christie (photobiology) and Murphy (auxin) to understand how these processes are linked to higher plant phototropism
Collaborator Contribution Expertise and work from Christie and Murphy used to publish new research and review articles
Impact Research published in PLoS Biol., 9(6): e1001076; and reviewed in Am. J. Bot. 100, 35-46. Data presented at many international scientific meetings.
Start Year 2006
 
Description Justyna Labuz 
Organisation Jagiellonian University
Country Poland 
Sector Academic/University 
PI Contribution We have successfully engineered the activity of phototropin receptors to modulate plant growth.
Collaborator Contribution Justyna Labuz has characterised chloroplast movement responses.
Impact A manuscript based on our work has been submitted to PNAS.
Start Year 2017
 
Description Noriyuki Suetsugu 
Organisation University of Kyoto
Country Japan 
Sector Academic/University 
PI Contribution This works is focussed on characterising NPH3/RPT2 proteins in plants and their contribution to optimising photosynthetic light capture.
Collaborator Contribution Dr Suetsugu visited and worked with us as a JSPS research fellow.
Impact One review has been published and another manuscript submitted to Plant Physiology.
Start Year 2016
 
Description Phosphoproteomics 
Organisation University of Dundee
Country United Kingdom 
Sector Academic/University 
PI Contribution Christie and Lamont are collaborating to identify phosphorylation control of higher plant phototropism.
Collaborator Contribution Christie is leading the research and Lamont is providing expertise and facilities to characterise phosphorylation events associated with this process.
Impact Research published in Mol. Plant 1, 178-194 and in several review articles. Data has been presented at numerous international scientific conferences.
Start Year 2006
 
Description 6th and 7th Edition Plant Physiology and Development 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact Worked with other editors and authors to formulate chapters for the teaching text book Plant Physiology.

Edition still in press so difficult to gage at present but should provide an instrumental guide for school pupils and students.
Year(s) Of Engagement Activity 2015,2016,2017
 
Description Biochemist article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Article for the Biochemist magazine to inform readers of recent advances in phototropism research.

Article has stimulated email request for further information.
Year(s) Of Engagement Activity 2013
 
Description Chair of the GRC on Photosensory Receptors and Signal Transduction 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I organised this biennial meeting which was attended by academics, students and from Industry as well as NASA. The meeting was highly successful based on questionnaire feedback and will run again in two years time.
Year(s) Of Engagement Activity 2016
 
Description Edinburgh (2013) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Talk and session sparked discussion and questions.

Meeting stimulated interactions with Prof. Christian Fankauser (Lausanne). A manuscript relating to this work has been submitted.
Year(s) Of Engagement Activity 2013
 
Description Gatsby Summer School 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact I gave a plenary lecture and participated in the summer school to encourage teachers and students to consider plant science and photo biological research.
Year(s) Of Engagement Activity 2015
URL http://www.slcu.cam.ac.uk/outreach/gatsbyplants
 
Description Gif-sur-Yvette (2013) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Gif-sur-Yvette, France. Invited speaker, CNRS. Talked gave rise to questions and discussions afterwards. Also acted on panel for thesis committee defence.

This visit has stimulated interactions with French colleagues and has attracted a student internship visit from the Lyon who will begin in 2015.
Year(s) Of Engagement Activity 2013
 
Description Industry day 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Supporters
Results and Impact Participated in workshop focussed on attracting commercial interest/awareness.

Has attracted translational interest. Collaborations with Pirbright have led to publication and talks with Ingenza initiated in using technologies derived from our research.
Year(s) Of Engagement Activity 2012
 
Description Invited seminar speaker, Freie Universitat Berlin 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited as one of two plenary speakers to a workshop on photobiology organised by PhD students at the Freie Universitat Berlin. Participated in discussions of future research directions
Year(s) Of Engagement Activity 2015
 
Description Japan 2012 (Nara) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Talks and meeting stimulated discussions.

Scientific interactions with Japan established and requests for research expertise materials.
Year(s) Of Engagement Activity 2012
 
Description Japan 2013 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Plenary speaker. Talked sparked research questions and discussions afterwards.

Talk has stimulated exchange visit between Shinichiro Inoue (Nagoya) and Glasgow and prompted his visit.
Year(s) Of Engagement Activity 2013
 
Description Manchester 2013 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Invited seminar speaker. Talk and meetings with members of the department stimulated discussions.

Has instigated collaborative interactions between Glasgow and Manchester.
Year(s) Of Engagement Activity 2013
 
Description Milan 2014 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Invited seminar speaker at the University of Milan. Talk sparked discussion and questions afterwards.

Has led to collaborative research between myself and Prof. Anna Moroni, which will be submitted soon.
Year(s) Of Engagement Activity 2014
 
Description Nagoya Institute of Technology International Symposium on Frontier Materials 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited speaker and workshop participant
Year(s) Of Engagement Activity 2016
 
Description Royal Society 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Other audiences
Results and Impact Invited to serve on the Royal Society University Research Fellowship (URF) Biological Panel as of 2015.

Yet to implement.
Year(s) Of Engagement Activity 2015
 
Description Seeing 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Participated in talks and laboratory exercises for the voluntary undergraduate teaching course SEEING! aimed at promoting plant science and cell biology.

Assessed by student questionnaire and feedback. Improved student's outlook on plant science. Attracted students to become involved in summer research projects.
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,2011,2012,2013,2014
 
Description Summer students 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact Host summer students to gain laboratory experience and educate them about plant science.

Can be effective in changing students views towards plant science and help make them decide to pursue this as a degree or career.
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,2011,2012,2013,2014
 
Description Tuebingen 2012 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Invited seminar speaker. Talk and meetings with department members stimulated discussions.

Led to masters student to visit my lab and conduct research as part of an internship placement.
Year(s) Of Engagement Activity 2012
 
Description University open day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Talks provided pupils with insight and advice decide research degree choices.

University continues to attract a a higher number of school pupils to study at Glasgow.
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,2011,2012,2013,2014