The Arabidopsis AtRGGA protein is involved in post-transcriptional regulation of gene expression during salt stress

Soil salinity reduces crop yields and limits available land for agriculture. Understanding themolecular mechanisms of plant salt stress response is becoming increasingly important. RNAregulatory mechanisms such as synthesis, transport, translation, stability and degradation of transcripts participate in the modulation of abiotic stress responses. RNA binding proteins play an important role in such mechanisms, but relatively few have been characterized in plants so far. In a previous study, we have shown the involvement of AtRGGA, encoding a glycine-rich RNA-bindingprotein, in responses to drought and salt stress (Ambrosone et al., 2015).an Electrophoresis Mobility Shift Assays (EMSA) with total RNA usingrecombinant His-RGGA showed that RGGA is capable of binding RNA in vitro.Here we presentprotein and RNA interaction studies using AtRGGA as a bait. Results from these experiments point to a role for AtRGGA in post-transcriptional control of gene expression during osmotic stress. To identify protein partners of AtRGGA, yeast two-hybrid screening was performed using an Arabidopsis cDNA library. Most of the identified proteins are involved in salt stress response, such as BODYGUARD (BDG1, At1g64670), essential for cuticle biogenesis and regulator of the Abscisic Acid (ABA) biosynthesis and signaling. Other putative partners include RNA-bindingproteins with a function in RNA export from the nucleus and involved in stress response. For the isolation of RNAs bound to AtRGGA, we performed a Ribonucleoprotein ImmunoPurification(RIP) assay. Immunopurification of FLAG-AtRGGA from stress-treated transgenic plants, followedby RNA extraction and qRT-PCR allowed the identification and quantitative comparison of RNAassociated to AtRGGA under salt stress (120 mM NaCl) in vivo. Interestingly, RNA corresponding to the transcription factor DREB2A, a key regulator of drought stress responses, was significantly enriched in the AtRGGA-immunopurified samples under stress condition compared to total RNA.Taken together, our results indicate that AtRGGA could be involved in RNA export from thenucleus into the cytoplasm, and that AtRGGA is biased in the RNAs it binds, including key saltstress response transcripts.Additional experiments aimed at i) confirming putative interactions identified by yeast two-hybrid and ii) sequencing and quantification of transcripts bound to AtRGGA will address thesehypotheses.