Light, temperature and circadian clock signal integration during leaf senescence

叶片衰老是一个积极的过程，涉及营养物质从年老的、光合作用有限的组织中重新动员到发育的植物结构中。它的特点是由于叶绿体的分解和叶绿素的降解而引起的叶片显黄。叶片衰老可由环境胁迫引起，如长时间的黑暗，并在高温下加速。在商业园艺中，切块产品的叶片衰老降低了作物质量和保质期，给种植者造成了重大的经济损失。在温暖和黑暗的条件下运输和储存农产品使这一问题更加严重，这就要求生产商和零售商投资于成本高昂且对环境不友好的制冷技术。可持续地延缓叶片衰老是生鲜食品行业的一个关键目标，但具有成本效益的实际解决方案仍然有限。在模式植物拟南芥中，黑暗诱导的叶片衰老是由光、温度和生物钟调节的转录因子光敏色素相互作用因子4 （PIF4）和PIF5促进的。Franklin实验室的研究表明，低剂量（非胁迫）UV-B光处理可以促进拟南芥幼苗中PIF4和PIF5蛋白的快速降解，并抑制PIF4和PIF5基因的表达。在商业温室中，UV-B被玻璃过滤，而在垂直农场中，它不是园艺照明的组成部分。因此，在商业园艺中使用的大多数受保护的生长环境中都不存在UV-B。我们有初步的证据表明，采收前短时间（4小时）低剂量UV-B处理可以显著减少在较高温度下储存的离体拟南芥叶片和子叶的黑暗诱导衰老。这种处理抑制了关键的衰老调节因子ORE1的表达，并延缓了叶绿素的降解。这项工作将剖析光、温度和生物钟控制离体拟南芥叶片暗致衰老的分子信号通路。除了进一步深入了解关键发育过程的调控机制外，这项工作还将为利用采前和采后光处理延缓作物黑暗诱导的叶片衰老提供策略。我们的初步数据表明，收获前UV-B处理可以延缓黑暗诱导的小火箭（Eruca sativa）叶片衰老，支持我们的方法。总的来说，提出的工作将提供一个分子框架来解决可持续粮食储存的关键问题。

Leaf senescence is an active process involving the remobilisation of nutrients from older, photosynthetically limited tissues to developing plant structures. It is characterised by striking leaf yellowing resulting from the dismantling of chloroplasts and degradation of chlorophyll. Leaf senescence can be induced by environmental stress, such as prolonged darkness and is accelerated at high temperature. In commercial horticulture, leaf senescence in cut produce reduces crop quality and shelf-life, resulting in significant economic losses to growers. This problem is exacerbated by the transport and storage of produce in warm and dark conditions, requiring producers and retailers to invest in costly and environmentally unfriendly refrigeration technologies. Sustainably delaying leaf senescence is a key objective for the fresh food industry, yet cost-effective, practical solutions remain limited. In the model plant Arabidopsis thaliana, dark- induced leaf senescence is promoted by the light, temperature and circadian clock-regulated transcription factors, PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5. The Franklin lab has shown that low dose (non-stressful) UV-B light treatment can promote rapid degradation of PIF4 and PIF5 proteins and suppress the expression of PIF4 and PIF5 genes in Arabidopsis seedlings. UV-B is filtered by glass in commercial greenhouses and is not a component of horticultural lighting in vertical farms. As such, UV-B is absent in the majority of protected growing environments used in commercial horticulture. We have preliminary evidence that a short (4 hour) preharvest treatment of low dose UV-B can significantly reduce dark-induced senescence in detached Arabidopsis leaves and cotyledons stored at warmer temperatures. This treatment supresses the expression of the key senescence regulator, ORE1 and delays chlorophyll degradation. The proposed work will dissect the molecular signalling pathways through which light, temperature and the circadian clock control dark-induced senescence in detached Arabidopsis leaves. In addition to furthering mechanistic insight into the regulation of a key developmental process, the work will inform strategies for using pre and postharvest light treatments to delay dark-induced leaf senescence in crops. Our preliminary data suggest that preharvest UV-B treatment can delay dark-induced senescence in young rocket (Eruca sativa) leaves, supporting our approach. Overall, the proposed work will provide a molecular framework to address a key problem in sustainable food storage.