Professor Mark Tester
Federation Fellow (Australian Research Council)
Australian Centre for Plant Functional Genomics, Adelaide , Australia
Web site:
http://plantscience.acpfg.com.au
E-mail : mark.tester@acpfg.com.au
The big question
Coordinated responses by the whole plant to environmental stimuli are essential to allow plants to respond appropriately to changes in their environment, yet our understanding at the molecular and cellular levels of high level co-ordination processes remains minimal. One system in which such research is potentially tractable is that of the control of accumulation of inorganic nutrients and toxins by the plant. The measurable output, shoot nutrient concentration, is easily obtained, yet this is clearly the outcome of a complex series of events which take place at all levels (molecule, cell, tissue, organ and organism). Furthermore, variations in the supply of these nutrients can be manipulated easily, so whole plant responses to this challenge can readily be probed. The ultimate intellectual aim of my research programme is to understand mechanisms of long-distance communication within plants by studying genes which co-ordinate whole plant responses that are induced to correct inappropriate nutrient concentrations in the shoot.
The immediate aim of research in my laboratory is to elucidate the molecular mechanisms that enable certain plants to thrive in sub-optimal soil conditions, such as high salinity or acidity - where excess accumulation in the shoot of toxic elements such as Na and Al limit growth. The applied outputs of this programme are to genetically modify crop plants in order to increase their productivity on such soils; and to increase the mineral content of their seeds. The current focus is on salinity tolerance, so the solutes being studied are Na + , Cl - and boric acid, complemented by work with Ca 2+ , increasing concentrations of which usually ameliorate sodium toxicity.
Many components of salinity tolerance of a whole plant require particular characteristics of specific cells, rather than generic properties of all cells within a plant. Most notably, to facilitate Na + exclusion from the shoot (commonly associated with salinity tolerance), Na + would need to be pumped out of cells in the outer part of the root, but into cells in the inner part of the root, adjacent to the xylem (to maintain low Na + in the xylem and thus low delivery to the shoot). This cell specificity of Na + transport, essential for Na + tolerance, is likely to be the main reason why previous attempts to use standard biotechnology for generating salt tolerant plants have mostly failed. The novel approach being employed in my laboratory is the study and manipulation of ion transport in specific cell types within the plant, particularly in the root.
Cell specific transport has been studied in my laboratory using electrophysiological techniques for several years. Recently, we have started to exploit a novel system for controlling gene expression to generate transgenic plants with altered levels of expression of Na + transporters in specific cell types. This new approach to the study of salinity tolerance is expected to provide insights into the molecular basis for salinity tolerance, and to provide the technology for the generation of salt tolerant crops in the future. To this end, we are continuing to characterise the transport pathways for the entry and intra-plant distribution of the target solutes, with a view to future cell-specific misexpression of appropriate genes.
Such work is now being complemented by more genomic level approaches, namely the random activation of genes in specific cell types; and the screening of mutants with randomly activated genes for abnormal accumulations of solutes in the shoot using ICP-MS. This programme has the added value of providing material of interest to human nutritionists, as plants with increased accumulation of valuable elements such as Fe, I and Zn will be identified. Deficiencies in these elements generate some of the most significant health problems globally.
Most research in my laboratory employs the classic model plant, Arabidopsis thaliana, whose small size and sequenced genome pre-disposes it to molecular and genetic studies. However, about three years ago I decided to begin using rice, as an important crop in its own right, but also as a powerful model cereal and monocotyledon which is not as extensively studied as Arabidopsis. This move is proving timely, as transformation technologies for rice have improved vastly and the public genome sequence is expected to become available within the next year or so.
The short-term goals
To meet our research aims, work must be on two complementary fronts:
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A physiological characterisation of the transport processes underlying probable tolerance processes (using mainly electrophysiological and radioactive tracer techniques).
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A molecular biological manipulation of the genes responsible for controlling the transport processes, to test their effects on tolerance.
My intention in the next three years is to increase the emphasis on the latter approach, whilst trying to maintain strength in the former. We need to continue the characterisation of the transport pathways for the entry and intra-plant distribution of the target solutes (Na + , Cl - , B(OH) 3 ), in parallel with cell-specific misexpression of both plant genes and more thoroughly characterised genes from animals. This involves several projects, almost all of which can be extended by future workers.
- Mark Tester
- John Banfield
- Irina Abakumova Nutriome screen of Arabidopsis activation tagged lines
- Romola Davenport Na transport in higher plants
- Alex Johnson Enhancer trap lines in rice
- Matthew Gilliham MIFE in oocytes expressing GLRs
- Nerissa Hannink Nutriome screen of Arabidopsis activation tagged lines
- Lai-Hua Liu GLRs in Arabidopsis
- Pauline Essah Cell-specific gene-specific activation and silencing in rice
- Frances Tracy Effects of Na on cytosolic free Ca signals in Arabidopsis
- Ben Davies GLRs in Arabidopsis
- Gehan El-Hussieny Random gene activation in root epidermis and cortex of Arabidopsis
- Inge Skrumsager Møller Random gene activation in root stele of Arabidopsis
- Geraint Story Development of stress reporter lines of Arabidopsis
Currently active
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BBSRC, ' Generation of enhancer trap lines of rice ( Oryza sativa L.) expressing gal4 and gfp in specific cell types' (with JM Hibberd) £216,844
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BBSRC Research Development Fellowship, 'Changes in gene expression in single plant cells in response to stress' £ 94,576
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BBSRC, 'Use of vibrating multibarrelled ion-selective electrodes to identify ion species permeating nonselective ion channels from plants' £192,436
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2002 EU RTN, 'Novel ion channels in plants' (with B Müller-Röber et al.) €961,443
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BBSRC, 'The plant 'nutriome' accessed by an ICP-MS screen for unusual element accumulation in activation-tagged Arabidopsis mutants' (with RA Leigh) £387,316
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BBSRC, 'Discovery of genes controlling solute accumulation by random gene activation specifically in the stele of Arabidopsis' £177,668
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Alliance Franco-British Partnership Programme, with Dr E. Guiderdoni £ 1,875
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2003 Nuffield Foundation Undergraduate Research Bursary £ 1,597
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2004 ARC Federation Fellowship approx $3.0 m
Applications submitted or planned
- ARC grant, on effects of random gene activation in specific cell types on shoot solute accumulation in rice
| Techniques in the laboratory
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Our main tools are molecular and electrophysiological. Therefore the majority of work done in the laboratory involves the creation of transgenic plants and the application of patch clamp electrophysiology and radioactive tracers to explore ion transport within the plant.
- Specifically, techniques we currently use include:
- Cloning of genes encoding plant transporters into binary vectors and yeast and Xenopus expression vectors
- Transformation of Arabidopsis and rice
- Generation of families of Arabidopsis and rice mutants with cell-specific activation of random genes
- High throughput ICP-MS-based screening of mutants
- Unidirectional flux measurements, using radioactive tracers
- Patch clamp electrophysiology
- Ion flux estimation using MIFE
- Measurement of cytosolic free Ca 2+ using aequorin
Top three areas of knowledge
- Ion fluxes in plants
- Salinity tolerance in plants
- Plant electrophysiology
Top three technical skills
- Radioactive flux analyses
- Electrophysiology
- Analysis of plant growth experiments
| A statement on the most significant contributions to this research field
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Plant cation channels - influx
From my PhD thesis, a seminal review on ion channels ( New Phytol 114: 305). During my PhD, introduced use of artificial planar lipid bilayers ( Physiol Plant 91: 770) to study ion channels in endomembrane systems (e.g. thylakoids: Plant Physiol 91: 249) and rare ion channels (e.g. Ca 2+ channels: Planta 195: 478; et seq. ). Planar lipid bilayers facilitated study of nonselective cation channels (NSCCs: e.g. Plant Physiol 122: 823), work confirmed using more standard patch clamp electrophysiology (notably Plant Physiol 128: 379). This establishes the importance of NSCCs as the main functional Ca 2+ channels in plant cells; and as the major pathway for toxic Na + influx ( Annu Rev Plant Biol 53, 67).
Cell-specific processes in intact plants
The importance of cell-specific processes in controlling solute accumulation into the shoot is explained in recent reviews (e.g. J Exp Bot , 52, 445), in particular when considering salinity tolerance ( Ann Bot 91: 503). I was the first to address this electrophysiologically, with a comparison of maize cortex versus stele ( Plant J 8: 811; J Exp Bot 48: 839). Work in my laboratory found that K + channels in these two cell types are independently controlled by ABA ( Plant Physiol 116: 145). This approach is extended with expression of the Ca 2+ -sensitive photoprotein, aequorin, in the cytosol of specific cell types in Arabidopsis ( Plant J 23: 267).
Salinity tolerance - the current position
To complement the molecular cellular approaches described above, a molecular genetic approach is being initiated to probe the role of specific cell types in the control of solute accumulation in the shoot (explained in Part E). I started this programme in Cambridge , using Arabidopsis; and resources are being established to move this technology into rice.
Other evidence of impact and contributions to the field
I have just started an ARC Federation Fellowship, which builds on my award two years ago of a BBSRC Research Development Fellowship. During the past two years, I have been awarded five BBSRC research grants, with a total value of £1,057,849 ($Aus3.0m) and an EU collaborative grant (with Bernd Müller-Röber and others) of €961,443 ($Aus1.7m). I served on two BBSRC committees, for their Special Initiative on Biological Interactions in the Root Environment; and I was a core member of their Plant & Microbial Sciences Committee. Last year, I served on an International Review Committee for CNRS/INRA, France , for the review of their flagship plant science research centre in Montpellier , l'Unité Biochimie et Physiologie Moléculaire des Plantes. I am an associate editor of Plant, Cell & Environment , and referee for large numbers of international journals (including Nature Biotech, Science, EMBO J, PNAS USA, Plant Cell, Plant J, Plant Physiol ) and for funding bodies throughout the world (e.g. NSF, USDA, USDoE, Israel Science Foundation, ARC).
In 1998, I organised the major triennial conference in our field, the 11th International Workshop on Plant Membrane Biology, Cambridge (with 450 participants). I have been a member of the International Organising Committee for the next two meetings in that series. I routinely chair sessions at national and international conferences, and am a Discussion leader at the next Gordon Conference on drought and salinity. In addition to seminars and offered presentations at conferences, I have been an invited keynote or plenary speaker at several conferences in the past three years (Society for Experimental Biology; ComBio2001; Gordon Conference on drought and salinity; International Workshop on Plant Membrane Biology, Montpellier , International Plant Growth Substances Meeting, Canberra ).
| Publications - Last 5 Years
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Journal articles
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Demidchik, V., Essah, P. & Tester, M . (2004) Glutamate activates sodium and calcium currents in the plasma membrane of Arabidopsis root cells. Planta , in press
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*Essah, P.A., Davenport , R.J. & Tester, M . (2003) Sodium influx and accumulation in Arabidopsis thaliana . Plant Physiology 133: 307-318
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*Berthomieu, P., Conéjéro, G., Nublat, A., Brackenbury, W.J., Lambert, C., Savio, C., Uozumi, N., Oiki, S, Yamada, K., Cellier, F., Gosti, F., Simmonneau, T., Essah, P.A., Tester, M ., Véry, A.A., Sentenac, H., Casse, F. (2003) Functional analysis of AtHKT1 in Arabidopsis shows that Na + recirculation by the phloem is crucial for salt tolerance. EMBO Journal 22: 2004-2014
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Tester, M . (2002). Some GM facts. Science 298: 1341-1342 *Tester, M. & Davenport, R.J. (2002) Na + transport and Na + tolerance in higher plants. Annals of Botany 91: 503-527
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*Demidchik, V., Bowen, H., Maathuis, F., Shabala, S., Tester, M ., White, P.J. & Davies, J., (2002) Arabidopsis thaliana root nonselective cation channels mediate calcium uptake and are involved in growth. Plant Journal 32: 799-808 *Demidchik, V.V., Shabala, S., Coutts, K.B., Tester, M . & Davies, J.M. (2002) Free oxygen radicals regulate plasma membrane Ca 2+ - and K + -permeable channels in plant root cells activation by hydroxyl radicals mediates early plant stress responses. Journal of Cell Science 116: 81-88
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*Demidchik, V. & Tester, M. (2002) Sodium fluxes through non-selective cation channels in the plasma membrane of protoplasts from Arabidopsis thaliana roots.
Plant Physiology 128: 379-387
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*Demidchik, V., Davenport , R.J. & Tester, M. (2002) Nonselective cation channels.
Annual Reviews of Plant Biology 53 , 67-107
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*Kronzucker, H.J., Britto, D.T., Davenport , R.J. & Tester, M . (2001) Ammonium toxicity and the real cost of transport. Trends in Plant Sciences 6, 335-337
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* Tester, M. & Leigh, R.A. (2001) Partitioning of transport processes in roots. Journal of Experimental Botany , 52, Roots Special Issue, 445-457
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*Lacombe, B., Becker, D., Hedrich, R., Chiu, J., DeSalle, R., Heinemann, S., Hollmann, M., Kwak, J., Le Novere, N., Nam , H.G., Sakmann, B., Schroeder, J.I., Spalding, E.P., Tester, M ., Turano, F.J. & Coruzzi, G. (2001) On the identity of plant glutamate receptors. Science 292, 1486-1487
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Tester, M . (2001) Depolarising the GM debate. New Phytologist 149, 9-16
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*Kiegle, E., Moore , C., Haseloff, J., Tester, M . & Knight, M. (2000) Cell-type specific calcium responses to drought, NaCl, and cold in Arabidopsis root: a role for endodermis and pericycle in stress signal transduction. Plant Journal 23: 267-278
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*White, P.J., Piñeros, M., Tester , M. & Ridout, M.S. (2000) Cation permeability and selectivity of a root plasma membrane calcium channel. Journal of Membrane Biology 174: 71-83
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* Davenport , R.J. & Tester, M. (2000) A weakly voltage-dependent, nonselective cation channel mediates toxic sodium influx in wheat. Plant Physiology 122: 823-834
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*Kiegle, E., Gilliham, M., Haseloff, J & Tester, M. (2000) Hyperpolarisation- activated calcium currents found only in cells from the elongation zone of Arabidopsis thaliana roots. Plant Journal 21: 225-229
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Tester, M. (1999) Seeking clarity over the safety of GM foods. Nature 402, 575
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Tester, M. (1999) Hand over your clones or lose your reputation. Nature 398, 657
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* Tester, M. (1999) Control of long-distance K + transport by ABA . Trends in Plant Sciences 4: 5-6
Other publications
| Ten career-best publications
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I include a brief background to explain the reasons for inclusion of each paper, as the judgement of 'best' depends on a range of measures (journal impact factor, citations, citations per year, personal opinion).
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Tester, M. (1990) Plant ion channels: whole cell and single-channel studies. The New Phytologist 114: 305-340. The only comprehensive review of plant ion channels, it was timely and is my most cited paper (227 citations).
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White, P.J. & Tester, M. (1992) Potassium channels from the plasma membrane of rye roots characterized following incorporation into planar lipid bilayers. Planta 186: 188-202.
The first single-channel characterisation of a nonselective cation channel in plants, the likely pathway for Na + influx into roots, cited 51 times.
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Zorec, R. & Tester, M. (1992) Cytoplasmic calcium stimulates exocytosis in a plant secretory cell. Biophysical Journal 63: 864-867.
The first direct measure of exocytosis in plants, cited 45 times.
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Homann, U. & Tester, M. (1997) Ca 2+ -independent and Ca 2+ /GTP-binding protein-controlled exocytosis in a plant cell. Proceedings of the National Academy of Sciences of the USA 94: 6565-6570.
Rigorous follow-up of the previous paper.
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Roberts, S.K. & Tester, M. (1995) Inward and outward K + -selective currents in the plasma membrane of protoplasts from maize root cortex and stele. Plant Journal 8: 811-825.
Electrophysiology from the early days of my group in Cambridge , and my first work focussing on the importance of contrasting processes in inner and outer halves of the root. Cited 70 times.
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Piñeros, M. & Tester, M. (1995) Characterization of a voltage-dependent Ca 2+ -selective channel from wheat roots. Planta 195: 478-488.
A careful study of single Ca 2+ channels in plants to date, and highly cited - 88 times.
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Kiegle, E., Gilliham, M., Haseloff, J & Tester, M. (2000) Hyperpolarisation-activated calcium currents found only in cells from the elongation zone of Arabidopsis thaliana roots. Plant Journal 21: 225-229.
Delving more deeply into cell-specific processes, exploiting enhancer trap lines expressing GFP in specific cell types to study for the first time Ca 2+ -selective channels in different cell types. Already cited 33 times.
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Kiegle, E., Moore , C., Haseloff, J., Tester, M. & Knight, M. (2000) Cell-type specific calcium responses to drought, NaCl, and cold in Arabidopsis root: a role for endodermis and pericycle in stress signal transduction. Plant Journal 23: 267-278.
First use of enhancer trapped lines with cell-specific expression of GAL4 to drive cell-specific expression of YFP-aequorin to study cell-specific responses of cytosolic Ca 2+ to salinity. Already cited 42 times. All lines were designed and generated in my laboratory.
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Davenport , R.J. & Tester, M. (2000) A weakly voltage-dependent, nonselective cation channel mediates toxic sodium influx in wheat. Plant Physiology 122: 823-834.
A definitive identification of the importance of nonselective cation channels in the influx of Na + from saline soils. Already cited 44 times.
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Demidchik, V., Davenport , R.J. & Tester, M. (2002) Nonselective cation channels. Annual Reviews of Plant Biology 53 , 67-107.
The first review of nonselective cation channels in plants. Already cited 25 times, in just over its first year.
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