Dr Penelope Smith

Penny Smith Photo
Position: Senior Lecturer
Phone: +61 2 9036 7169
Fax: +61 2 9351 4771
Mobile Phone: N/A
Email: penny.smith@sydney.edu.au
Location: Room 248
Address: A12 - Macleay, The University of Sydney, NSW 2006 Australia 

Current Research

Transport Proteins on the Symbiosome membrane of soybean

Transport Proteins on the Symbiosome membrane of soybean

Bacteroids (the symbiotic form of rhizobia) inside the infected nodule cells are surrounded by a membrane of plant origin that effectively segregates the bacteroids from the plant cytoplasm and controls the type and quantity of compounds that pass between the partners. The bacteroids enclosed by the plant envelope form the symbiosome, a facultative organelle (part prokaryote, part eukaryote), which is the fundamental N2-fixing unit within legume nodules. Rhizobia are totally dependent upon their plant hosts for nutrients when living within the nodule. The symbiosome membrane (SM) has selective permeability to metabolites by grace of a unique suite of proteins encoded in the host cell nucleus and targeted to the symbiosome. My research group studies mechanisms for transport of nutrients across the symbiosome membrane and the assimilation of the nitrogen fixed by rhizobia as well as the mechanism by which proteins translated in the cytoplasm move to their subcellular location in nodules.

More details see:

Purine biosynthesis in legume nodules: regulation of nitrogen assimilation and targeting of enzymes to organelles

I am studying the regulation genes encoding enzymes involved in purine biosynthesis in legume nodules. Tropical legumes assimilate ammonia formed by nitrogenase through synthesis of purines in nodules. Rates of purine biosynthesis in these tissues are 104 times greater than in meristematic tissues of the plant. We have identified both transcriptional and post-translational regulation of the pathway by studying the effects of short and long-term deprivation of N2.

The purine biosynthesis pathway is localised in both plastids and mitochondria in nodules of tropical legumes. We are studying the localisation of the enzymes to these organelles using GFP fusions.

Small RNAs as long distance signalling molecules in phloem of plants?

MicroRNAs (miRNAs) are a recently discovered class of small non-coding RNA that play a significant regulatory role in both plants and animals by targeting mRNAs for cleavage or translational repression. In plants many of the targets of miRNAs are mRNAs encoding transcription factors that play a role in developmental processes but it is now becoming obvious that they regulate many processes and may also have a role in regulating plant responses to stress. We are investigating the translocation of miRNAs in phloem of Lupinus albus, a plant from which phloem exudate can easily be isolated, and in the model plant Arabidopsis thalliana. We have cloned miRNAs from phloem and characterised their distribution in L.albus. We are now using the information gained to develop strategies to prove transport of miRNAs in Arabidopsis where mutants in miRNA biogenesis are available. Assays to study phloem loading and unloading of miRNAs are being developed and the proteins responsible for transport cloned.

More details see:

Aniline blue staining of lupin pedicel showing vascular tissue including phloem Phloem bleeding from lupin flowers A grafted Arabidopsis plant used to study translocation of signals in phloem

Molecular analysis of lupin seeds components including allergens

There is increasing interest in lupin seed proteins and milk as human foods and a number of health benefits have been associated with its consumption. High protein and fibre (and low allergen content) are important characteristics for lupins as human food. However we have very little information about what it is that determines the final components of the lupin grain or what the key components in the mature seed that give the positive (and negative) health benefits. In this project lupin seed components are being characterised at different developmental stages using genomic and proteomic approaches. In particular the allergens of lupin are being characterised to determine if there is cross-reactivity with peanut allergens. We have also produced transgenic lupins modified at different stages of pod set and seed development. The long-term aim is to determine the regulatory processes involved in formation of protein and fibre and use this knowledge to improve the seed for human consumption.

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Selected Publications

  • Carrie C, Murcha MW, Kuehn K, Duncan O, Barthet M, Smith PM, Eubel H, Meyer E, Day DA, Millar H, Whelan J. (2008) Type II NAD(P)H dehydrogenases are targeted to mitochondria and chloroplasts or peroxisomes in Arabidopsis thaliana. FEBS Letters 582:3073-3079.
  • Goggin DE, Mir G, Smith WB, Stuckey MS and Smith PMC (2008) Proteomic analysis of lupin seed proteins to identify conglutin β as an allergen, Lup an 1. Journal of Agricultural and Food Chemistry 56:6370-7.
  • Armstrong AF, Badger MR, Day DA, Barthet MM, Smith PMC, Millar AH, Whelan J and Atkin AK (2008) Dynamic changes in the mitochondrial electron transport chain underpinning cold acclimation of leaf respiration. Plant Cell and Environment 31:1156-1169
  • Liu DYT, Kuhlmey BT, Smith PMC, Day DA, Faulkner CR, Overall RL (2008) Reflection across plant cell boundaries in confocal laser scanning microscopy. Journal of Microscopy. 231:349-357.
  • Atkins CA and Smith PMC (2007) Translocation in Legumes: Assimilates, Nutrients, and Signaling Molecules. Plant Physiology 144:550-61.
  • Bussell JD, Hall DJ, Mann AJ, Goggin DE, Atkins CA and Smith, PMC (2005) Alternative splicing of the Vupur3 transcript in cowpea produces multiple mRNA species with a single protein product that is present in both plastids and mitochondria. Functional Plant Biology.32: 683-693.
  • Clements JC, Buirchell BC, Yang H, Smith PMC, Sweetingham MW and Smith CG (2005) Genetic Resources, Chromosome Engineering, and Crop Improvement" Series-II Grain Legume. In: Lupins, Genetic resources, Chromosome Engineering and Crop Improvement, Series II, Grain Legumes, Ed. Singh, R.J. CRC Press, NY. p231-323.
  • Goggin DE, Lipscombe R, Fedorova E, Millar H, Mann AJ, Atkins CA and Smith PMC (2003) Dual localization and targeting of aminoimidazole ribonucleotide synthetase in cowpea. Plant Physiology 131: 1033-1041.
  • Smith PMC, Winter H, Storer PJ, Bussell JD, Schuller KA and Atkins CA (2002) Effect of Short-Term N2 Deficiency on Expression of the Ureide Pathway in Cowpea (Vigna unguiculata L.) Root Nodules. Plant Physiology 129:1216-1221.
  • Smith PMC and Atkins CA (2002) Purine Biosynthesis: Big in Cell Division- Even Bigger in Nitrogen Assimilation. Plant Physiology 128: 793-802.
  • Smith PMC, Mann AJ, Goggin DE and Atkins CA (1998) AIR synthetase in cowpea nodules : a single gene product targeted to two organelles? Plant Molecular Biology 36: 811-820.
  • Atkins CA, Smith PMC and Storer PJ (1997) Re-examination of the intracellular localization of de novo purine synthesis in cowpea nodules. Plant Physiology 113: 127-135.
  • Pigeaire A, Abernathy D, Smith PM, Simpson K, Fletcher N, Lu C-Y, Atkins CA and Cornish E (1997) Routine transformation of a grain legume crop (Lupinus angustifolius L.) via Agrobacterium tumefaciens- mediated gene transfer to shoot apices. Molecular Breeding. 3:341-349.