title: TcNPR3 from Theobroma cacao functions as a repressor of the pathogen defense response.
abstract: BACKGROUND
  Arabidopsis thaliana (Arabidopsis) NON-EXPRESSOR OF PR1 (NPR1) is a transcription coactivator that plays a central role in regulating the transcriptional response to plant pathogens. Developing flowers of homozygous npr3 mutants are dramatically more resistant to infection by the pathogenic bacterium Pseudomonas syringae, suggesting a role of NPR3 as a repressor of NPR1-mediated defense response with a novel role in flower development.
  
  
  RESULTS
  We report here the characterization of a putative NPR3 gene from the tropical tree species Theobroma cacao (TcNPR3). Like in Arabidopsis, TcNPR3 was constitutively expressed across a wide range of tissue types and developmental stages but with some differences in relative levels compared to Arabidopsis. To test the function of TcNPR3, we performed transgenic complementation analysis by introducing a constitutively expressing putative TcNPR3 transgene into an Arabidopsis npr3 mutant. TcNPR3 expressing Arabidopsis plants were partially restored to the WT pathogen phenotype (immature flowers susceptible to bacterial infection). To test TcNPR3 function directly in cacao tissues, a synthetic microRNA targeting TcNPR3 mRNA was transiently expressed in cacao leaves using an Agrobacterium-infiltration method. TcNPR3 knock down leaf tissues were dramatically more resistance to infection with Phytophthora capsici in a leaf bioassay, showing smaller lesion sizes and reduced pathogen replication.
  
  
  CONCLUSIONS
  We conclude that TcNPR3 functions similar to the Arabidopsis NPR3 gene in the regulation of the cacao defense response. Since TcNPR3 did not show a perfect complementation of the Arabidopsis NPR3 mutation, the possibility remains that other functions of TcNPR3 remain to be found. This novel knowledge can contribute to the breeding of resistant cacao varieties against pathogens through molecular markers based approaches or biotechnological strategies.
authors: Zi
authors: Z
authors: Shi
authors: Yufan
authors: Y
authors: Zhang
authors: Siela N
authors: SN
authors: Maximova
authors: The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA. mjg9@psu.edu.
authors: Mark J
authors: MJ
authors: Guiltinan
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry; D001681:Biological Assay; D002099:Cacao / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D060467:Disease Resistance / Q000235:genetics / Q000276:immunology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D017343:Genes, Plant / Q000235:genetics; D005816:Genetic Complementation Test; D054884:Host-Pathogen Interactions / Q000276:immunology*; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D018515:Plant Leaves / Q000235:genetics / Q000276:immunology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D044224:Pseudomonas syringae / Q000276:immunology*; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; C517740:NPR3 protein, Arabidopsis; D010940:Plant Proteins