REACTIVE OXYGEN SPECIES (ROS) AND SALICYLIC ACID (SA) SIGNAL PROLINE ACCUMULATION IN PLANT:PATHOGEN INCOMPATIBLE INTERACTIONS

FABRO, GEORGINA; PAVET, VALERIA; KOVACZ, IZABELLA; SZABADOS, LÁSZLÒ2; ALVAREZ, M.E

Bariloche, Argentina

Congreso; XXXIX REUNION ANUAL SAIB (SOCIEDAD ARGENTINA DE BIOQUIMICA Y BIOLOGIA MOLECULAR); 2003

SAIB

L-Proline (Pro) accumulation is a classical response against abiotic stresses (drought, salinity and cold). Although its protective role is not well understood, it is thought to function as compatible osmolyte and ROS scavenger. We recently demonstrated that Pro accumulation is also triggered by biotic injuries. Pro content increases in A. thaliana tissues developing incompatible plant:pathogen interactions with avirulent races of Pseudomonas syringae activating a Hypersensitive Response (HR). Pro increase in HR correlates with transcriptional activation of Pro biosynthetic AtP5CS2 and catabolic ProDH genes. AtP5CS2 GUS and AtP5CS2 LUC transgenes are induced inside and around HR lesions where Pro also accumulates. To investigate whether Pst -induced Pro enhancement requires signaling components of the HR, we evaluated the role of ROS and SA in the activation of this novel response. We quantified Pro levels and AtP5CS2 expression in: i) SA- and ROS-treated wild type plants, ii) SA-deficient mutants. We analyzed both responses in interactions involving two avirulence genes (Pst avrRpm1 and Pst avrRps2) which have different SA requirements. As other defenses, Pro accumulation was more sensitive to SA deficiency when elicited by Pst avrRps2 . Meanwhile, exogenous ROS activate both Pro enhancement and AtP5CS2 expression. SA may then potentiate Pro accumulation affecting early steps of the defense cascade, probably involving ROS as intermediate signal.