The protein phosphatase subunit PP2A‐B′γ is required to suppress day length‐dependent pathogenesis responses triggered by intracellular oxidative stress

Abstract

SummaryOxidative stress responses are influenced by growth day length, but little is known about how this occurs. A combined reverse genetics, metabolomics and proteomics approach was used to address this question in Arabidopsis thaliana.A catalase-deficient mutant (cat2), in which intracellular oxidative stress drives pathogenesis-related responses in a day length-dependent manner, was crossed with a knockdown mutant for a specific type 2A protein phosphatase subunit (pp2a-b′c). In long days (LD), the pp2a-b′c mutation reinforced cat2-triggered pathogenesis responses.In short days (SD), conditions in which pathogenesis-related responses were not activated in cat2, the additional presence of the pp2a-b′c mutation allowed lesion formation, PATHOGENESIS-RELATED GENE1 (PR1) induction, salicylic acid (SA) and phytoalexin accumulation and the establishment of metabolite profiles that were otherwise observed in cat2 only in LD. Lesion formation in cat2 pp2a-b′c in SD was genetically dependent on SA synthesis, and was associated with decreased PHYTOCHROME A transcripts. Phosphoproteomic analyses revealed that several potential protein targets accumulated in the double mutant, including recognized players in pathogenesis and key enzymes of primary metabolism.We conclude that the cat2 and pp2a-b′c mutations interact synergistically, and that PP2A-B ′c is an important player in controlling day length-dependent responses to intracellular oxidative stress, possibly through phytochrome-linked pathways.

Intracellular Redox Compartmentation and ROS-Related Communication in Regulation and Signaling

“…Excess ROS production in the peroxisomes triggers oxidative stress responses that are dependent on growth daylength . Growth in long days allows peroxisomal H 2 O 2 to trigger PR responses that are not apparent in plants grown in short days, an effect that is linked to protein phosphorylation status (Li et al, 2014). Longday contexts also favor the development of lesions in response to equal-time exposure of Arabidopsis to ozone, a condition that triggers an initial ROS burst and oxidative stress in the apoplast (Dghim et al, 2013).…”

Protein phosphatase 2A regulatory subunits affecting plant innate immunity, energy metabolism, and flowering time – joint functions among B'η subfamily members

“…11,12 Moreover, B'g was proposed to have a role in daylength-dependent oxidative stress. 13 Another interesting study revealed a role for PP2A in negative regulation of PTI. 14 The study concluded that PP2A holoenzymes containing B'h and B'z regulate the activation of the patternÀrecognition receptors (PRR) complexes by controlling the phosphorylation status of PRR-positive regulator BAK1.…”

Towards Understanding Extracellular ROS Sensory and Signaling Systems in Plants

“…Knockout cat2 plants show constitutive SA-dependent defense responses and cell death under long-day conditions. However, under short-day photoperiods SA signaling and cell death are not induced in the cat2 mutants, despite of the prevalence of oxidative stress [78][79][80]. We have shown with a combination of genetic, proteomic, and metabolomic analyses that in the cat2 mutant a cytoplasmic protein phosphatase 2A regulatory subunit B (PP2A-B ) is required to suppress the day length-dependent, salicylic acid mediated pathogenesis responses triggered by organellar ROS signals [78,81].…”

“…The formation of photorespiratory ROS signals in the peroxisomes seems to play a major role in photoperioddependent signaling [77,78]. Similarly to re, day length also conditions the ROS-dependent phenotype of Arabidopsis CATALASE2 (CAT2) knock-out mutants which accumulate photorespiratory H 2 O 2 in the peroxisomes [79].…”

“…Based on this, we can position RE in regulatory network which functionally interconnects photoperiod and hormonal interactions with cross-compartmental ROS signaling which may trigger stress-induced morphogenic responses and activate protective mechanisms in plants [73,[76][77][78].…”