Dorothee Staiger

SUMMARY The importance of RNA‐binding proteins (RBPs) for plant responses to environmental stimuli and development is well documented. Insights into the portfolio of RNAs they recognize, however, clearly lack behind the understanding gathered in non‐plant model organisms. Here, we characterize binding of the circadian clock‐regulated Arabidopsis thaliana GLYCINE‐RICH RNA‐BINDING PROTEIN 7 ( At GRP7) to its target transcripts. We identified novel RNA targets from individual‐nucleotide resolution UV crosslinking and immunoprecipitation (iCLIP) data using an improved bioinformatics pipeline that will be broadly applicable to plant RBP iCLIP data. 2705 transcripts with binding sites were identified in plants expressing At GRP7‐GFP that were not recovered in plants expressing an RNA‐binding dead variant or GFP alone. A conserved RNA motif enriched in uridine residues was identified at the At GRP7 binding sites. NMR titrations confirmed the preference of At GRP7 for RNAs with a central U‐rich motif. Among the bound RNAs, circadian clock‐regulated transcripts were overrepresented. Peak abundance of the LHCB1.1 transcript encoding a chlorophyll‐binding protein was reduced in plants overexpressing At GRP7 whereas it was elevated in atgrp7 mutants, indicating that LHCB1.1 was regulated by At GRP7 in a dose‐dependent manner. In plants overexpressing At GRP7, the LHCB1.1 half‐life was shorter compared to wild‐type plants whereas in atgrp7 mutant plants, the half‐life was significantly longer. Thus, At GRP7 modulates circadian oscillations of its in vivo binding target LHCB1.1 by affecting RNA stability.