Department of Plant Sciences

Dr Julia Davies

Find out more about Julia Davies and her Group or email Julia.Davies@plantsci.cam.ac.uk

Project titles:

  1. Environmental signalling in a marine diatom
  2. Root hair growth for crop improvement
  3. Extracellular ATP as a novel regulator of signalling and development
  4. Channel formation by annexins; plant nanopores?
  5. Annexin-mediated signalling in stress and defence
  6. Nitric oxide regulation of calcium channels and signalling
  7. Chloroplast Ca2+ signalling
 

Project Title: Environmental signalling in a marine diatom

Supervisor: Dr Julia Davies

Project outline:

Marine diatoms are responsible for approximately a quarter of global photosynthetic carbon fixation. Despite this, our understanding of diatom physiology remains limited. Iron is a key limiting nutrient in the oceans and understanding the cellular mechanisms underlying the response of diatoms to iron-limitation will provide important information on the factors limiting global primary productivity. Analyses of the response of the marine diatom Phaeodactylum tricornutum to iron limitation indicate oxidative stress and Ca2+ signalling play important roles (1, 2). This project will explore the function of two putative annexins in the P. tricornutum genome which are strongly upregulated following iron limitation. Annexins are soluble, multifunctional proteins which have proposed roles in coordinating reactive oxygen species and Ca2+ signalling networks (3). Annexins are capable of calcium-dependent membrane attachment or insertion and can form calcium-permeable channels in plants and animals (3). Advanced molecular genetic techniques available in P. tricornutum will enable localisation of annexins through fusion to green fluorescent protein (GFP) and targeted knockdown of annexin expression through RNA interference. Annexin protein sequences will be analysed for conserved sequences, particularly metal binding sites. Heterologously expressed annexins will be tested for peroxidase and calcium channel activity to ascertain whether they could participate in oxidative stress protection (3) and calcium signalling (2). The project is jointly supervised by Dr. Glen Wheeler, Plymouth Marine Laboratory.

  1. PNAS USA 105 10438
  2. Science 288 2363
  3. New Phytologist 189 40

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Root hair growth for crop improvement

Supervisor: Dr Julia Davies

Project outline:

Generating hairier, bushier roots should improve nutrient and water capture. This is particularly important for Brassicas as they lack mycorrhizal symbionts. Root hair elongation is accompanied by oscillations in cytosolic free calcium at the apex (1). Plasma membrane calcium channels will be involved in generating these oscillations. We have identified three calcium channels (2-4) using electrophysiology and need to understand their regulation, contribution to calcium oscillations and molecular identities. This project will use Arabidopsis mutants, electrophysiology and calcium imaging to address these problems.

  1. PNAS. USA 104: 20996-21001
  2. PNAS USA 97: 9801
  3. Nature 422: 442
  4. New Phytologist 179: 378

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Extracellular ATP as a novel regulator of signalling and development

Supervisor: Dr Julia Davies

Project outline:

Since we discovered that extracellular ATP can regulate plant cytosolic free Ca2+ (1) it has become clear that this signalling system is involved in pathogen responses, development and cell death (2,3). How it all works remains unclear. G proteins have a possible role in transmitting the signal to plasma membrane Ca2+ channels and from there the link is to production of reactive oxygen species (3). In this project, the signalling jigsaw will be pieced together. By concentrating on specific cell types such as the Arabidopsis root hair or guard cell, the plasma membrane Ca2+ channels responding to extracellular ATP and ADP can be characterized (4,5). Using channel, G protein and NADPH oxidase mutants will allow the impact of signalling elements on cytosolic Ca2+, reactive oxygen species, transcripts and cellular response to be established.

  1. Plant Physiology 133, 456
  2. Plant Cell 17, 3019
  3. Trends in Cell Biology 20, 601
  4. Plant Journal 58, 903
  5. Plant Physiology 156,1375

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Channel formation by annexins; plant nanopores?

Supervisor: Dr Julia Davies

Project outline:

Annexins are soluble, multifunctional proteins which have proposed roles in coordinating reactive oxygen species and Ca2+ signalling networks (1). Annexins are capable of calcium-dependent membrane attachment or insertion and can form calcium-permeable channels in plants and animals (1). We have shown previously that maize annexin channel activity is strongly influenced by the lipid environment (2,3). We need now to understand how annexin channels form and are regulated in order to relate to in vivo context and exploit the possibility that they may act as nanopores for biotechnological application. This project is in collaboration with Dr. Ulrich Keyser, Department of Physics.

  1. New Phytologist 189 40
  2. Plant Cell 21: 479
  3. Plant Physiology 152: 1824

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Annexin-mediated signalling in stress and defence

Supervisor: Dr Julia Davies

Project outline:

Annexins are soluble, multifunctional proteins which have proposed roles in coordinating reactive oxygen species and Ca2+ signalling networks (1). Annexins are capable of calcium-dependent membrane attachment or insertion and can form calcium-permeable channels in plants and animals (1). As such, annexins should have an impact on calcium-mediated signalling in plants but this remains unexplored. Arabidopsis mutants transformed to express cytosolic calcium indicators will permit the role of annexins in generating calcium signals in response to environmental/defence stimuli to be addressed.

  1. New Phytologist 189 40

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Nitric oxide regulation of calcium channels and signalling

Supervisor: Dr Julia Davies

Project outline:

NO acts a signalling agent in both animal and plant cells, elevating cytosolic free Ca2+ as a second messenger (1,2). In animals, NO is involved in neurotransmission, inflammation and muscle function. A range of animal cation channel proteins are regulated by NO (through nitrosylation) to facilitate Ca2+ flux. These include voltage-gated Ca2+ channels and ryanodine receptors. In plants, NO is involved in gas exchange, pollen tube and root growth, drought and thermotolerance plus defence against pathogens. The molecular identity of NO-regulated plant Ca2+ channels remains largely unknown and to date, the effects of NO on root Ca2+ channels has not been reported. In this study, the effects of NO on the activity of the Arabidopsis root plasma membrane Ca2+ channels we have previously characterised will be tested (3-5). Additionally, channels identified from nitrosylation studies will provide the entry route into discovering their molecular identity. Measuring changes in cytosolic free Ca2+ in loss of function mutants will enable cellular context to be established.

  1. Besson-Bard et al. (2008) Annual Review of Plant Biology 59, 21
  2. Hess et al. (2005) Nature Reviews of Molecular Cell Biology 6, 150
  3. Demidchik et al. (2002) Plant Journal Journal 32, 799
  4. Foreman et al. (2003) Nature 422, 442
  5. Demidchik et al. (2007) Plant Journal 49, 377

See Research or email: Julia.Davies@plantsci.cam.ac.uk


 

Project Title: Chloroplast Ca2+ signalling

Supervisor: Dr Julia Davies

Project outline:

Recent evidence points to chloroplast involvement in Ca2+ signalling events in the cytosol. The chloroplast is now implicated in control of guard cell movements and gas exchange through sensing changes in stromal Ca2+ (1,2). Stromal Ca2+ levels also change during light/dark transition and could be involved in signalling for control of photosynthesis (3). How is stromal Ca2+ regulated? This project will involve characterising the Ca2+ channels of the Arabidopsis thylakoid membrane and examining their regulation by reactive oxygen species. Channel mutants will be transformed to express apoaequorin in the stroma so that their role in regulating stromal Ca2+ can be deduced. Mutants will also be phenotyped to assess impact on photosynthesis, morphology, gas exchange and productivity.

  1. Nomura et al. (2008) Plant J. 58, 988
  2. Weinl et al. (2008) New Phytol. 179, 675
  3. Sai and Johnson (2002) Plant Cell 14, 1279

See Research or email: Julia.Davies@plantsci.cam.ac.uk