# Interaction of OsCSN2 with OsCULs Under Red and Far-Red Light Regulates Stem and Coleoptile Growth in Rice

## TL;DR

This study explores how OsCSN2 interacts with other proteins in rice under red and far-red light to regulate stem and coleoptile growth.

## Contribution

The study reveals novel regulatory mechanisms of OsCSN2 under specific light conditions in rice growth and development.

## Key findings

- OsCSN2 regulates GA homeostasis and photomorphogenesis under natural light via SLR1 and COP1-HY5.
- Under red light, OsCSN2 promotes GA accumulation and stem growth while inhibiting coleoptile elongation.
- Lysine mutations in OsCSN2 alter interactions with CRLs, affecting ubiquitination and degradation of key growth regulators.

## Abstract

CSN2, a highly conserved subunit of the COP9 signalosome (CSN), serves as the primary binding site for Cullin in the CSN complex. This interaction, dependent on lysine residues, positions CSN2 as a key player in approximately 20% of CRL-mediated ubiquitination reactions, a critical regulatory pathway for growth, development, and cellular processes in eukaryotes. While the role of CSN2 in human cells has been partially characterized, its function in rice (OsCSN2) remains poorly understood. Building on our previous findings regarding OsCSN2 function under natural light, this study investigates its regulatory mechanisms in rice seedlings under red and far-red light conditions. We demonstrate that under natural light, OsCSN2 mainly affects rice GA homeostasis by regulating the expression of SLR1 and influences rice photomorphogenesis by regulating the expression of the COP1-HY5 complex, thereby controlling rice growth through two pathways. Unlike under natural light, under red light, OsCSN2 promotes the expression of OsGID1, enhances the interaction between OsGID1 and OsSLR1, and promotes GA accumulation and OsPIL14 expression, leading to rice stem growth and inhibition of coleoptile elongation. Under far-red light, OsCSN2 mainly promotes the expression of OsCOP1, increasing the formation of the COP1-HY5 complex, which inhibits photomorphogenesis and coleoptile elongation. Lysine site mutations in OsCSN2 affect the interaction between the OsCSN complex and CRLs, regulating CRL-mediated ubiquitination reactions, promoting the ubiquitin-mediated degradation of OsSLR1 and OsCOP1, and thus promoting rice growth. These findings not only elucidate the functional roles of OsCSN2 in rice growth regulation but also provide valuable genetic resources for breeding rice varieties with enhanced agronomic traits.