Dr Steve Roberts
Senior Lecturer
Office C18
Division of Biomedical and Life Sciences
Faculty of Health and Medicine
Lancaster University
Lancaster
LA1 4YQ
UK
Tel: +44 1524 593145
Fax: +44 1524 593192
E-mail: s.k.roberts@lancaster.ac.uk
Research Interests
The major research interests of my group concern the regulation of ion transport across the biological membranes of plant and fungal cells. Current areas of interest include:
Organic acid secretion and nutrient acquisition by higher plants
Organic acid secretion from higher plant roots into the soil solution plays an important role in nutrient acquisition and metal ion detoxification. Surprisingly, the pathways by which organic acids cross the plasma membrane of root cells are not well characterised and little is known of the molecular mechanisms that regulate the exudation of organic acids from roots. We are currently characterising anion channel activity in the root of Arabidopsis and, in that process, have recently identified a novel organic acid efflux channel in the plasma membrane of Arabidopsis epidermal root cells (Diatloff et al., 2004; see Publications). This channel is regulated by soil phosphate availability, suggesting that this novel transporter is likely to play a key role in phosphate acquisition. Research is currently ongoing to establish further its role in higher plant physiology.
Calcium signalling in filamentous fungi
Fungi are a diverse but discrete group of organisms with a myriad of activities, many of which impact both directly and indirectly on mankind. Thus understanding how these organisms respond and adapt to their environment is of fundamental importance. Cytosolic Ca2+ has been established as a ubiquitous intracellular signal molecule, essential for the transduction of a wide variety of environmental stimuli in eukaryotic cells. However, despite a strong body of evidence showing key roles for Ca2+ signal transduction in filamentous fungi, our understanding of Ca2+ signalling in these organisms is not well developed. One of the main reasons for this is our current ignorance of Ca2+-permeable channel activity (which is responsible for mediating cytosolic Ca2+ signalling events) in filamentous fungi. Work is ongoing to address this fundamental gap in our knowledge; namely, to identify and functionally characterise Ca2+ permeable channels in filamentous fungi. This work is taking advantage of recent developments in fungal genomics, initially leading to the identification of a number of candidate genes that are likely to encode Ca2+ permeable ion channels (and thus play key roles in Ca2+ signalling) in the model filamentous fungus, Aspergillus nidulans. A multidisciplinary approach, combining a range of molecular biological and cell biological techniques, is being employed.
Trichome physiology (in collaboration with Dr Martin McAinsh)
Trichomes are cellular extensions of the epidermis layer of higher plant leaves. Investigations in our laboratories show that trichomes accumulate a variety of toxic and essential metal ions. However, little is know about the mechanisms that mediate metal ion accumulation in trichomes. Current work aims to identify and functionally characterise the transporters responsible for cation accumulation in trichomes. The long-term goal of this research is to assess the potential of exploiting trichome physiology in phytoremediation strategies.
Anion channel function in filamentous fungi
Anion channels play essential roles in many aspects of animal and plant cell biology. However, little is known of their roles in fungi. We have used a laser ablation technique to gain access to the cell plasma membrane and patch clamp experiments have shown plasma membrane anion channels to be abundant in Aspergillus nidulans (Roberts et al., 1997; see Publications). We have recently identified a number of anion channel encoding genes in Aspergillus nidulans; the physiological roles of these channels are currently being investigated by phenotypic analysis of anion channel null mutants (for example, Oddon et al., 2004; see Publications).
Education
1990 BSc Biochemistry, Lancaster University
1994 PhD Cell physiology, Lancaster University/Marine Biological Association, Plymouth
Academic Positions
1993 - 1996 Research Associate, Plant Sciences, University of Cambridge
1996 - 2000 Research Associate, University of York
2000 - 2004 Wellcome Trust Research Career Development Fellowship, Lancaster University
2004 - present Lecturer, Lancaster University
Awards/Grants
2000: Four year Wellcome Trust Research Career Development Fellowship “The role of plasma membrane ion channels in fungal growth - potential targets for fungicides”. (£311,656).
2001: Three year BBSRC grant “Release of organic acid to the rhizosphere: a role for anion channels”. (£209,216).
2001: BBSRC Committee Studentship “Anion transport in Arabidopsis root”
2003: Two year BBSRC grant “Developing Pichia pastoris as a heterologous expression system for ion transporters”. (£105,848).
2004: Two year Knowledge Transfer Partnership Award funded by DTI and Micap Limited to develop novel encapsulation technology to protect and control the release of active ingredients from yeast. (£135,323).
Recent Publications
Diatloff E, Forde BG, Roberts SK. (2006) Expression and transport characterisation of the wheat low-affinity cation transporter (LCT1) in the methylotrophic yeast Pichia pastoris. Biochemical and Biophysical Research Communications 344, 807 - 813.
Peiter E, Fischer M, Sidaway K, Roberts SK, Sanders D (2005) The Saccharomyces cerevisiae Ca2+ channel Cch1pMid1p is essential for tolerance to cold stress and iron toxicity. FEB Letters 579 (25): 5697-5703.
Oddon, D., Diatloff, E. and Roberts, S. K. (2005). CLC chloride channels play an essential role in copper homeostasis in Aspergillus nidulans. Eukaryotic Cell (submitted).
Diatloff, E., Roberts, M.R., Sanders, D. and Roberts, S.K. (2004). Characterisation of anion channels in the plasma membrane of Arabidopsis epidermal root cells and the identification of a citrate-permeable channel induced by phosphate starvation. Plant Physiology 136, 4136 – 4149.
Eugene Diatloff, Dietmar Geiger, Lijun Shang, Rainer Hedrich and Stephen K Roberts (2004). Differential regulation of K+ channels in Arabidopsis epidermal and stelar root cells. Plant, Cell and Environment 27, 980 - 990.
Chang-Hyo Goh, Ki-Hong Jung, Stephen K. Roberts, Martin R. McAinsh, Alistair M. Hetherington, Youn-il Park, Kye-Hong Suh, Gynheung An, and Hong Gil Nam (2004). Mitochondria Provide the Main Source of Cytosolic ATP for Activation of Outward-rectifying K+ Channels in Mesophyll Protoplast of Chlorophyll-deficient Mutant Rice (OsCHLH) Seedlings. J. Biol. Chem. 279, 6874 - 6882.
Roberts SK (2006). Plasma membrane anion channels in higher plants and their putative functions in roots. New Phytologist 169: 647 - 666. (Invited Review)
Roberts, S.K. (2003). TOK homologue in Neurospora crassa: First cloning and functional characterisation of an ion channel in a filamentous fungus. Eukaryotic Cell 2, 181-190.
Roberts, S. K., Dixon, G. K. Fischer, M. and Sanders, D. (2001). A novel low-affinity H+-Cl- co-transporter in yeast: characterisation by patch clamp Mycologia 93 626-633.
Roberts, S. K. and Snowman, B. (2000). The effects of ABA on channel-mediated K+ transport across higher plant roots. J. Exp. Bot. 51, 1585-1594.
Roberts, S. K., Dixon, G. K. Fischer, M. and Sanders, D. (1999). Divalent cation block of inward currents and low-affinity uptake in Saccharomyces cerevisiae. J. Bacteriol. 181, 291-297.
Roberts, S. K. (1998). Regulation of K+ channels in maize roots by water stress and ABA. Plant Physiol. 116, 145-153.
Roberts, S. K., Dixon, G., Dunbar, S. J. and Sanders, D. (1997). Laser ablation of the cell wall and localised patch clamping of the plasma membrane in the filamentous fungus Aspergillus: characterisation of an anion selective efflux channel. New Phytol. 137, 579 - 585.
Roberts, S. K. and Tester, M. (1997). Permeation of Ca2+ and monovalent cations through an outwardly-rectifying channel in maize root stelar cells. J. exp. Bot. 48, 839 - 846.
Roberts, S. K. and Tester, M. (1997). A patch clamp study of Na+ transport in maize roots. J. exp. Bot. 48, 431 - 440.
Roberts, S. K and Tester, M. (1995). Inward and outward K+-selective currents in the plasma membrane of protoplasts from maize root cortex and stele. The Plant Journal 8, 811-825.
Roberts, S. K. and Brownlee, C. (1995). Calcium influx, fertilisation potential and egg activation in Fucus serratus. Zygote 3, 191-197.
Roberts, S. K., Gillot, I. and Brownlee, C. (1994). Cytoplasmic calcium and Fucus egg activation. Development 120, 155-163.
Roberts, S. K., Berger, F. and Brownlee, C. (1993). The role of Ca2+ in signal transduction following fertilisation in Fucus serratus. J. Exp. Biol. 184, 197-212.
Taylor, A. R., Roberts, S. K., Brownlee, C. (1992). Calcium and related channels in fertilisation and early development of Fucus zygotes. Phil. Trans. R. Soc. Lond. B. 338, 97-104.