title: Two Theobroma cacao genotypes with contrasting pathogen tolerance show aberrant transcriptional and ROS responses after salicylic acid treatment.
abstract: Understanding the genetic basis of pathogen susceptibility in various crop plants is crucial to increasing the stability of food, feed, and fuel production. Varietal differences in defence responses provide insights into the mechanisms of resistance and are a key resource for plant breeders. To explore the role of salicylic acid in the regulation of defence in cacao, we demonstrated that SA treatment decreased susceptibility to a pod rot pathogen, Phytophthora tropicalis in two genotypes, Scavina 6 and Imperial College Selection 1, which differ in their resistance to several agriculturally important pathogens. Transient overexpression of TcNPR1, a major transcriptional regulator of the SA-dependent plant immune system, also increased pathogen tolerance in cacao leaves. To explore further the genetic basis of resistance in cacao, we used microarrays to measure gene expression profiles after salicylic acid (SA) treatment in these two cacao genotypes. The two genotypes displayed distinct transcriptional responses to SA. Unexpectedly, the expression profile of the susceptible genotype ICS1 included a larger number of pathogenesis-related genes that were induced by SA at 24h after treatment, whereas genes encoding many chloroplast and mitochondrial proteins implicated in reactive oxygen species production were up-regulated in the resistant genotype, Sca6. Sca6 accumulated significantly more superoxide at 24h after treatment of leaves with SA. These experiments revealed critical insights regarding the molecular differences between cacao varieties, which will allow a better understanding of defence mechanisms to help guide breeding programmes.
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Fister
authors.affiliation: Center for Genome Research and Biocomputing, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Shawn T
authors.initials: ST
authors.lastname: O'Neil
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: The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Yufan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Center for Genome Research and Biocomputing, Oregon State University, Corvallis, OR 97331, USA Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Tyler
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA The Department of Plant Science, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Guiltinan
authors.affiliation: The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA The Department of Plant Science, The Pennsylvania State University, University Park, PA 16802, USA snm104@psu.edu.
authors.forename: Siela N
authors.initials: SN
authors.lastname: Maximova
mesh_terms: D002099:Cacao / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D060467:Disease Resistance; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D008969:Molecular Sequence Data; D010838:Phytophthora / Q000235:genetics / Q000502:physiology*; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids; D017382:Reactive Oxygen Species / Q000378:metabolism; D020156:Salicylic Acid / Q000494:pharmacology*; D017422:Sequence Analysis, DNA
chemical_list: D010940:Plant Proteins; D017382:Reactive Oxygen Species; D020156:Salicylic Acid
keywords: Cacao; Phytophthora tropicalis; TcNPR1.; pathogenesis-related genes; reactive oxygen species; salicylic acid