CISP, an Intrinsically Disordered Cold-Inducible Barley Protein, Functions As a Small RNA Chaperone.

Low temperatures are a major environmental stress that limits plant growth and development. Understanding the molecular mechanism of cold tolerance is therefore essential for improving crop performance through molecular breeding. In this study, we focused on CISP, a small, previously uncharacterized protein, specifically induced in barley roots under low temperature conditions, and investigated its potential role in cold tolerance. Heterologous expression of CISP in Escherichia coli enhanced late-phase bacterial growth at low temperatures compared with the wild-type strain. Similarly, overexpression of CISP in Arabidopsis thaliana, which lacks an apparent ortholog, improved seedling growth under low temperature conditions. These results suggest that CISP can promote growth of heterologous organisms used in this study at low temperature environments. To investigate its molecular function, we performed RNA chaperone assays using RNA beacons that tend to form stable secondary structures. CISP reduced the formation of RNA secondary structures and facilitated their destabilization, indicating RNA chaperone-like activity. CISP is a basic, low-molecular-weight protein containing an intrinsically disordered region (IDR) at its N-terminus but lacking canonical RNA-binding domains such as the cold shock domain (CSD) or RNA recognition motif (RRM). Our findings therefore suggest that CISP may represent a previously uncharacterized type of RNA chaperone. This study provides new insights into the structure and function of CISP and its potential contribution to cold tolerance in barley.