title: Protocol: a fast and simple in situ PCR method for localising gene expression in plant tissue.
abstract: BACKGROUND
  An important step in characterising the function of a gene is identifying the cells in which it is expressed. Traditional methods to determine this include in situ hybridisation, gene promoter-reporter fusions or cell isolation/purification techniques followed by quantitative PCR. These methods, although frequently used, can have limitations including their time-consuming nature, limited specificity, reliance upon well-annotated promoters, high cost, and the need for specialized equipment. In situ PCR is a relatively simple and rapid method that involves the amplification of specific mRNA directly within plant tissue whilst incorporating labelled nucleotides that are subsequently detected by immunohistochemistry. Another notable advantage of this technique is that it can be used on plants that are not easily genetically transformed.
  
  
  RESULTS
  An optimised workflow for in-tube and on-slide in situ PCR is presented that has been evaluated using multiple plant species and tissue types. The protocol includes optimised methods for: (i) fixing, embedding, and sectioning of plant tissue; (ii) DNase treatment; (iii) in situ RT-PCR with the incorporation of DIG-labelled nucleotides; (iv) signal detection using colourimetric alkaline phosphatase substrates; and (v) mounting and microscopy. We also provide advice on troubleshooting and the limitations of using fluorescence as an alternative detection method. Using our protocol, reliable results can be obtained within two days from harvesting plant material. This method requires limited specialized equipment and can be adopted by any laboratory with a vibratome (vibrating blade microtome), a standard thermocycler, and a microscope. We show that the technique can be used to localise gene expression with cell-specific resolution.
  
  
  CONCLUSIONS
  The in situ PCR method presented here is highly sensitive and specific. It reliably identifies the cellular expression pattern of even highly homologous and low abundance transcripts within target tissues, and can be completed within two days of harvesting tissue. As such, it has considerable advantages over other methods, especially in terms of time and cost. We recommend its adoption as the standard laboratory technique of choice for demonstrating the cellular expression pattern of a gene of interest.
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, University of Adelaide, Glen Osmond, SA, Australia.|Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Asmini
authors.initials: A
authors.lastname: Athman
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Perth, WA, Australia.
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Tanz
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, University of Adelaide, Glen Osmond, SA, Australia.|Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Vanessa M
authors.initials: VM
authors.lastname: Conn
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, University of Adelaide, Glen Osmond, SA, Australia.|Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Jordans
authors.affiliation: Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.|Adelaide Microscopy Waite Facility, University of Adelaide, Glen Osmond, SA, Australia.
authors.forename: Gwenda M
authors.initials: GM
authors.lastname: Mayo
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, University of Adelaide, Glen Osmond, SA, Australia.|Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Weng W
authors.initials: WW
authors.lastname: Ng
authors.affiliation: ARC Centre of Excellence in Plant Cell Walls, University of Adelaide, Glen Osmond, SA, Australia.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Burton
authors.affiliation: Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.|Centre for Cancer Biology, Division Immunology, Level 3, Frome Road, Adelaide, SA, Australia.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Conn
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, University of Adelaide, Glen Osmond, SA, Australia.|Waite Research Institute & School of Agriculture, Food and Wine, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.
authors.forename: Matthew
authors.initials: M
authors.lastname: Gilliham
keywords: Cell-specific localisation; Immunohistochemistry; In situ PCR; Plant tissue; RT-PCR