Dr Stephen Roberts

Membrane Transport Group

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.

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).

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.