Abstract
WRKY18, WRKY40 and WRKY60 are members of the WRKY transcription factor family and function as transcriptional regulators in ABA signal transduction in Arabidopsis thaliana. Here we show that WRKY18 and WRKY40, but not WRKY60, co-localise with PIF3, PIF4 and PHYB to Phytochrome B-containing nuclear bodies (PNBs). Localisation to the PNBs is phosphorylation-dependent and is inhibited by the general Ser/Thr-kinase inhibitor Staurosporine. Upon ABA treatment, WRKY40 relocalises from PNBs to the nucleoplasm in an OST1-dependent manner. This stimulus-induced relocalisation was not observed in response to other abiotic or biotic stimuli, including NaCl, MeJA or flg22 treatment. Bimolecular fluorescence complementation experiments indicate that while PIF3, PIF4 and PHYB physically interact in these bodies, PHYB, PIF3 and PIF4 do not interact with the two WRKY transcription factors, which may suggest a more general role for these bodies in regulation of transcriptional activity.
Highlights
The phytohormone Abscisic acid (ABA) regulates plant development and plant adaptation to environmental changes, i.e. seed maturation, seed germination and stomatal aperture regulation in response to drought or pathogens[1,2,3]
Propidium iodide (PI) cell death staining of Arabidopsis protoplasts showed that no cell death occurred in nuclei where WRKYs were localised to nuclear bodies (Figure S2)
WRKY transcription factors are regulated via transcriptional regulation, homo- and heterodimerisation, phosphorylation and epigenetic control[54]
Summary
The phytohormone Abscisic acid (ABA) regulates plant development and plant adaptation to environmental changes, i.e. seed maturation, seed germination and stomatal aperture regulation in response to drought or pathogens[1,2,3]. Besides ABF proteins, other transcription factor families play a role in ABA signalling, including MYB DOMAIN PROTEINS, ETHYLENE RESPONSE FACTORS, NUCLEAR FACTOR Y SUBUNIT A5 and WRKY DNA-BINDING PROTEINS (WRKY)[1,19,20,21,22,23,24]. Two WRKY proteins from Avena fatua (common wild oat), AfWRKY1 and AfWRKY2, which are orthologues of A. thaliana WRKY40, were among the first identified WRKY transcription factors They regulate gene expression during seed germination[25]. It was suggested that in response to ABA, these WRKY transcription factors translocate from nucleus to cytoplasm and interact with the H SUBUNIT OF MG-CHELATASE (GUN5), a putative ABA receptor protein[28]. Whether subnuclear relocalisation is a regulatory mechanism for ABA-regulated transcription factors has not been systematically studied. Subnuclear relocalisation might constitute a new regulatory mechanism, how ABA modulates transcription factor activity
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