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

Photoperiod is key to regulate plant development and reproduction. In rice (<i>Oryza sativa),</i> 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.

光周期是调控植物生长发育与生殖过程的关键因素。在水稻（Oryza sativa）中，长日照（LD）可延长营养生长阶段，而短日照（SD）则通过叶片光信号感知介导的调控通路加速开花进程。本研究采用质谱技术，对长、短日照条件下培养的水稻叶片蛋白质组进行分析，共鉴定到超过6000种蛋白质，其中部分蛋白质呈现光周期特异性表达谱。在长日照或短日照下富集的蛋白质中，超过半数由具有昼夜节律表达振荡特征的基因编码。一类被归为长日照“昼末蛋白”的亚群大多定位于叶绿体，其编码基因在当日结束时的表达水平更高。整体而言，长日照富集的蛋白质与碳、氮代谢过程密切相关，这与该阶段的生物量积累特征相符。与之相反，短日照条件会显著提升SCL和RSZ型富含丝氨酸-精氨酸（SR）剪接因子的丰度。这类蛋白质参与胁迫响应与生殖过程，提示上述过程的转录后调控可能与植物对光周期转变的适应过程相互交织。本研究为日长如何塑造叶片蛋白质组提供了全新见解，同时阐明了RNA加工在调控水稻响应开花诱导性短日照过程中的生理与发育响应方面的重要性。