title: Context of action of proline dehydrogenase (ProDH) in the Hypersensitive Response of Arabidopsis.
abstract: BACKGROUND
  Proline (Pro) dehydrogenase (ProDH) potentiates the oxidative burst and cell death of the plant Hypersensitive Response (HR) by mechanisms not yet elucidated. ProDH converts Pro into ∆1 pyrroline-5-carboxylate (P5C) and can act together with P5C dehydrogenase (P5CDH) to produce Glu, or with P5C reductase (P5CR) to regenerate Pro and thus stimulate the Pro/P5C cycle. To better understand the effects of ProDH in HR, we studied the enzyme at three stages of the defense response differing in their ROS and cell death levels. In addition, we tested if ProDH requires P5CDH to potentiate HR.
  
  
  RESULTS
  Control and infected leaves of wild type and p5cdh plants were used to monitor ProDH activity, in vivo Pro catabolism, amino acid content, and gene expression. Wild type plants activated ProDH at all HR stages. They did not consume Pro during maximal ROS accumulation, and maintained almost basal P5C levels at all conditions. p5cdh mutants activated ProDH as wild type plants. They achieved maximum oxidative burst and cell death levels producing normal HR lesions, but evidenced premature defense activation.
  
  
  CONCLUSIONS
  ProDH activation has different effects on HR. Before the oxidative burst it leads to Pro consumption involving the action of P5CDH. During the oxidative burst, ProDH becomes functionally uncoupled to P5CDH and apparently works with P5CR. The absence of P5CDH does not reduce ROS, cell death, or pathogen resistance, indicating this enzyme is not accompanying ProDH in the potentiation of these defense responses. In contrast, p5cdh infected plants displayed increased ROS burst and earlier initiation of HR cell death. In turn, our results suggest that ProDH may sustain HR by participating in the Pro/P5C cycle, whose action on HR must be formally evaluated in a future.
authors.forename: Mariela Inés
authors.initials: MI
authors.lastname: Monteoliva
authors.forename: Yanina Soledad
authors.initials: YS
authors.lastname: Rizzi
authors.forename: Nicolás Miguel
authors.initials: NM
authors.lastname: Cecchini
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Hajirezaei
authors.affiliation: Centro de Investigaciones en Química Biológica de Córdoba CIQUIBIC, UNC-CONICET, Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA Córdoba, Argentina. malena@mail.fcq.unc.edu.ar.
authors.forename: María Elena
authors.initials: ME
authors.lastname: Alvarez
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D011392:Proline / Q000378:metabolism; D011394:Proline Oxidase / Q000235:genetics / Q000378:metabolism*; D011758:Pyrroles / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D011758:Pyrroles; D017382:Reactive Oxygen Species; C015485:delta-1-pyrroline-5-carboxylate; D011392:Proline; D011394:Proline Oxidase