Gossens, R. | Search bioRxiv

bioRxiv2020

Arabidopsis Poly(ADP-ribose)-binding protein RCD1 interacts with Photoregulatory Protein Kinases in nuclear bodies

Continuous reprogramming of gene expression in response to environmental signals is required for plant survival in changing environment. One mechanism responsible for this is signaling through hub proteins that integrate external stimuli and transcriptional responses. RADICAL-INDUCED CELL DEATH1 (RCD1) functions as a nuclear hub protein, that interacts with a variety of transcription factors through its C-terminal RST domain and acts as a co-regulator of numerous stress responses in plants. Here, a previously unknown function for RCD1 as a novel plant poly(ADP-ribose) (PAR) reader protein is described. RCD1 localizes to specific locations inside the nucleus, in a PAR-dependent manner; its N-terminal WWE domain o binds PAR and together with the PARP-like domain determines its localization to nuclear bodies (NBs), which is prevented by inhibition of PAR synthesis. RCD1 also interacts with Photoregulatory Protein Kinases (PPKs) that co-localize with RCD1 in the NBs. The PPKs, that have been associated with circadian clock, abscisic acid, and light signaling pathways, phosphorylate RCD1 at multiple sites in the intrinsically disordered region between the WWE and PARP-like domains. This affects its stability and functions in the nucleus and1 provides a mechanism where the turnover of a PAR-binding transcriptional co-regulator is controlled by nuclear protein kinases.

plant biology↗

bioRxiv2019

Increased expression of mitochondrial dysfunction stimulon genes affects chloroplast redox status and photosynthetic electron transfer in Arabidopsis

Mitochondrial retrograde signals control expression of nuclear mitochondrial dysfunction stimulon (MDS) genes. Although MDS gene products mostly affect mitochondrial functions, they also influence production of reactive oxygen species (ROS) and redox status of chloroplasts. To study this inter-organellar interaction, we analysed the response of the Arabidopsis MDS-overexpressor mutant rcd1 to methyl viologen (MV), which catalyses electron transfer from Photosystem I (PSI) to molecular oxygen, generating ROS in Mehlers reaction. The response of plants to MV was investigated by imaging chlorophyll fluorescence in aerobic and hypoxic environments, and by membrane inlet mass spectrometry. Hypoxic treatment abolished the effect of MV on photosynthetic electron transfer in rcd1, but not in wild type. A similar reaction to hypoxia was observed in other MDS-activating lines and treatments. This suggests that MDS gene products contribute to oxygen depletion at the PSI electron-acceptor side. In unstressed growth conditions this MDS-related effect is likely masked by endogenous oxygen evolution and gas exchange with the atmosphere. In rcd1, altered Mehlers reaction coincided with more reduced state of the chloroplast NADPH-thioredoxin oxidoreductase C (NTRC) and its targets, suggesting that NTRC performs feedback control of photosynthesis. This regulation may represent a novel mechanism whereby mitochondrial retrograde signalling affects chloroplast functions.

plant biology↗