Photoperiodic regulation of rice leaf proteome reveals a splicing boost under short days

Photoperiod is key to regulate plant development and reproduction. In rice (Oryza sativa), long days (LD) prolong vegetative growth, while short days (SD) accelerate flowering, through a regulatory pathway stemming from light perception in the leaves. We analysed leaf proteomes of rice plants grown under LD and SD conditions using mass spectrometry and identified more than 6,000 proteins, with a subset presenting a photoperiod-specific profile. More than a half of the enriched proteins in either LD or SD was encoded by genes exhibiting circadian expression oscillations. A subgroup of LD "late-day proteins”, mostly chloroplastic, was encoded by genes with higher expression at the end of the day. Globally, LD-enriched proteins were associated to carbon and nitrogen metabolism, consistent with biomass accumulation during this stage. SD conditions, instead, induced a significant raise in the abundance of serine-arginine-rich (SR) splicing factors of the SCL and RSZ types. These proteins function in stress response and reproduction, implying that post-transcriptional regulation of these processes may intertwin with adaptation to the photoperiodic shift. This study provides novel insights into how daylength shapes the leaf proteome, informing about the importance of RNA processing in determining the physiological and developmental response to flowering-inductive, short photoperiods in rice.