Coping with stress: role of Arabidopsis phytoglobins in defence against Sclerotinia sclerotiorum

Abstract

Phytoglobins (Pgbs) are multifaceted stress-responsive proteins implicated in regulating various physiological and stress-responsive pathways in plants. Previous work has demonstrated NO dioxygenase and peroxidase-like activity of Arabidopsis phytoglobin 3 (AHb3) and its potential role in defense against Sclerotinia sclerotiorum. The work reported here highlights the significance of the other two classes of Arabidopsis phytoglobins (AHb1 and AHb2) in response to S. sclerotiorum. Constitutive expression of AHb1 (OEAHb1) and AHb2 (OEAHb2) conferred marginal tolerance towards S. sclerotiorum whereas respective knockdown (RNAi) lines displayed enhanced susceptibility, with AHb1 RNAi (RNAi-1) lines being more susceptible in comparison to AHb2 RNAi (RNAi-2) lines. Interestingly, transgenic lines with a simultaneous reduction in the transcripts of AHb1 and AHb2 (RNAi-F) displayed greater disease spread in comparison to individual knockdown lines indicative of their additive effect. The enhanced susceptibility upon pathogen challenge correlated with the elevated NO and H2O2 levels in these lines. Furthermore, detailed structural analysis hints towards an alternate mechanism of NO dioxyegnation by AHbs. Taken together, the current investigation illustrates the NO dioxygenase and peroxidase-like activity of AHbs and highlights their role in defense against stem rot pathogen S. sclerotiorum.