Light regulates nuclear detainment of intron-retained transcripts through COP1-spliceosome to modulate photomorphogenesis

Intron retention (IR) is the most common alternative splicing (AS) event in Arabidopsis. Increasing studies have demonstrated a major role of IR in gene expression regulation. The impacts of IR on plant growth and development, and response to environments remains under explored. Here, we found that IR functions directly in gene expression regulation on a genome-wide scale through detainment of the intron-retained transcripts (IRTs) in the nucleus. Through this mechanism, nuclear-retained IRTs can be kept away from translation. COP1-dependent light modulation of IRTs of light signaling genes, such as PIF4, RVE1, and ABA3, contribute to seedling morphological development in responding to changing light conditions. Further, light-induced IR changes are under the control of the spliceosome, and in part through COP1-dependent ubiquitination and degradation of DCS1, a plant-specific spliceosomal component. Our data suggests that light regulates the activity of the spliceosome and the consequent IRTs nucleus detainment to modulate photomorphogenesis through COP1.