Light, temperature and circadian clock signal integration during leaf senescence

叶片衰老是一个主动的过程，涉及营养物质从衰老的、光合作用有限的组织再动员到发育中的植物结构。其特征在于由于叶绿体的分解和叶绿素的降解而导致的显著的叶片黄化。叶片衰老可由环境胁迫诱导，如长时间的黑暗，并在高温下加速。在商业园艺中，切割产品中的叶片衰老降低了作物质量和货架期，给种植者造成重大经济损失。在温暖和黑暗的条件下运输和储存农产品，要求生产商和零售商投资于昂贵和对环境不友好的制冷技术，使这一问题更加严重。可持续地延迟叶片衰老是新鲜食品行业的一个关键目标，但具有成本效益的实用解决方案仍然有限。在模式植物拟南芥（Arabidopsis thaliana）中，黑暗诱导的叶衰老由光、温度和昼夜节律钟调节的转录因子植物色素相互作用因子4（PIF 4）和PIF 5促进。富兰克林实验室已经证明，低剂量（非胁迫）UV-B光处理可以促进拟南芥幼苗中PIF 4和PIF 5蛋白的快速降解，并抑制PIF 4和PIF 5基因的表达。UV-B在商业温室中被玻璃过滤，不是垂直农场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不存在UV-B。我们有初步的证据表明，短（4小时）低剂量UV-B的收获前处理可以显着减少黑暗诱导的衰老在离体拟南芥叶片和子叶储存在温暖的温度。这种处理抑制了关键衰老调节因子ORE 1的表达，并延迟了叶绿素的降解。拟开展的工作将剖析光、温度和生物钟控制离体拟南芥叶片暗诱导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来延迟作物黑暗诱导的叶片衰老提供信息。我们的初步数据表明，收获前的UV-B处理可以延迟黑暗诱导的衰老在年轻的火箭（芸芥）叶片，支持我们的方法。总的来说，拟议的工作将提供一个分子框架，以解决可持续食品储存中的一个关键问题。

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.