title: Protocol: transient expression system for functional genomics in the tropical tree Theobroma cacao L.
abstract: BACKGROUND
  Theobroma cacao L., the source of cocoa, is a crop of significant economic value around the world. To facilitate the study of gene function in cacao we have developed a rapid Agrobacterium-mediated transient genetic transformation protocol. Here we present a detailed methodology for our transformation assay, as well as an assay for inoculation of cacao leaves with pathogens.
  
  
  RESULTS
  Agrobacterium tumefaciens cultures are induced then vacuum-infiltrated into cacao leaves. Transformation success can be gauged 48 h after infiltration by observation of green fluorescent protein and by qRT-PCR. We clarify the characteristics of cacao leaf stages and demonstrate that our strategy efficiently transforms leaves of developmental stage C. The transformation protocol has high efficacy in stage C leaves of four of eight tested genotypes. We also present the functional analysis of cacao chitinase overexpression using the transient transformation system, which resulted in decreased pathogen biomass and lesion size after infection with Phytophthora tropicalis.
  
  
  CONCLUSIONS
  Leaves expressing transgenes of interest can be used in subsequent functional genetic assays such as pathogen bioassay, metabolic analysis, gene expression analysis etc. This transformation protocol can be carried out in 1 day, and the transgenes expressing leaf tissue can be maintained in petri dishes for 5-7 days, allowing sufficient time for performance of additional downstream gene functional analysis. Application of these methods greatly increases the rapidity with which candidate genes with roles in defense can be tested.
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, 422 Life Sciences Building, University Park, PA 16802 USA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Fister
authors.affiliation: Center for Applied Genetic Technologies, University of Georgia, Athens, GA 30602 USA.
authors.forename: Zi
authors.initials: Z
authors.lastname: Shi
authors.affiliation: Department of Electrical Engineering, Princeton University, Princeton, NJ 08544 USA.
authors.forename: Yufan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Botany and Plant Pathology, Center for Genome Research and Biocomputing, Oregon State University, Corvallis, OR 97331 USA.
authors.forename: Emily E
authors.initials: EE
authors.lastname: Helliwell
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, 422 Life Sciences Building, University Park, PA 16802 USA ; The Department of Plant Science, The Pennsylvania State University, University Park, PA 16802 USA.
authors.forename: Siela N
authors.initials: SN
authors.lastname: Maximova
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, 422 Life Sciences Building, University Park, PA 16802 USA ; The Department of Plant Science, The Pennsylvania State University, University Park, PA 16802 USA.
authors.forename: Mark J
authors.identifier: 0000-0003-0018-9846
authors.initials: MJ
authors.lastname: Guiltinan