Integration of seasonal signals through a two gene mutual repression switch in flower buds

植物利用季节线索温度和日照长度来确定它们从营养发育到生殖发育的过渡时间。天气和气候主要通过作用于这些信号通路来影响植物的发育，因此这是植物生物学中一个被高度研究的领域，从中出现了一个简单的范式，特别是在开花时间的控制方面。首先，FLC基因座感知长期温度，已知温度会影响FLC mRNA的转录（至少部分通过反义转录的调节），并导致FLC的表观遗传变化，反映季节性进展。在叶片中，FLC抑制第二个关键基因FT的表达，该基因在启动子处接收一个单独的信号，该信号反映了白天长度的测量。因此，温度和日长信息被认为在FT启动子上起加性作用，以改变植物的行为。FT是一种普遍的韧皮部移动季节性信号，在靶细胞中作为一种转录辅助因子，促进与夏季相关的发育程序。我们一直在研究同样的季节感应途径在控制种子休眠中的作用。这是一个母性过程，通过母亲利用她对季节信息的记忆来影响她的后代种子的休眠特征。通过这种方式，我们以前已经证明了植物的季节信息是从母亲传递给后代的。我们在这里提供的初步数据表明，尽管FLC和FT是植物中研究最深入的两个基因，但上述在FT启动子处逐步加性整合季节线索的范式不能解释我们对母体控制种子休眠的观察结果。具体来说，我们使用遗传学、基因表达分析和染色质免疫沉淀证明FLC是以前未被识别的FT的直接靶标，并且FT可以向反义FLC启动子传递日长度信息。因此，我们提出了一种新的植物季节感知模型，其中FT和FLC在经典的两基因相互抑制开关中相互抑制，这与被认为控制细胞周期进程的模型非常相似。这种开关可能具有非线性特性，并以不明显的方式整合日长和温度信息，以控制天气、季节和气候对植物发育的影响。第一个目标分为三个部分，旨在发现FT/FLC季节性开关的缺失组件，以及开关如何响应温度和光周期线索的季节性组合。我们关注的是冬季温度信号的时间和持续时间，以及它们的感知和功效如何通过发生在不同光周期的日子里而被修改。例如，在较长的白天经历的温度线索可能以不同的方式影响系统，而在非常短的冬季经历的温度线索。该提案的第二部分涉及识别控制开花后生殖发育的开关发生的组织。我们展示了惊人的初步证据，表明在花中，FT/FLC开关具有戏剧性的空间维度，环境线索和FT导致FLC mRNA表达从雌性器官切换到雄性器官。因此，我们假设控制种子休眠的环境信号在花蕾发育过程中被感知，同时也是第一个种子结构发育开始的时间。这很有趣，因为它使我们对一年生植物行为的理解与多年生植物的理解更加接近，多年生植物的芽在夏天发芽，但在寒冷的冬天打破这种休眠状态，使芽在春天发芽。我们将研究FLC在雄性和雌性花器官中异种表达对芽和种子发育和休眠的影响，并旨在揭示FLC表达在两个花器官之间响应季节信号而急剧转换的分子机制。

Plants use the seasonal cues temperature and day-length to time their transition from vegetative to reproductive development. Weather and climate affects plant development primarily by acting on these signalling pathways, and thus this is a highly studied area of plant biology from which a simple paradigm has emerged, especially in the control of time to flowering. Firstly, long term temperature is sensed by the FLC locus, with temperature known to affect FLC mRNA transcription (at least in part through regulation of antisense transcript) and resulting in epigenetic changes to FLC that reflect seasonal progression. In leaves FLC represses the expression of a second key gene FT, which receives a separate signal at its promoter that reflects a measurement of day length. Thus, temperature and day-length information is believed to act additively at the FT promoter to modify plant behaviour. FT is a general phloem-mobile seasonal signal, acting as a transcriptional co-factor in target cells to promote developmental programmes associated with summer.We have been studying the same seasonal sensing pathway in the control of seed dormancy. This is a maternal process through which the mother uses her memory of seasonal information to affect the dormancy characters of her progeny seed. In this way we have previously shown that seasonal information is passed from mother to progeny in plants. The preliminary data we present here show that although FLC and FT are two of the most intensively-studied genes in plants, the above paradigm of stepwise additive integration of seasonal cues at the FT promoter cannot explain our observations on the maternal control of seed dormancy. Specifically, we show using genetics, gene expression analysis and chromatin immunoprecipitation that FLC is a previously unrecognised direct target of FT, and that FT can deliver day-length information to the antisense FLC promoter. Thus we propose a new model for plant seasonal sensing in which FT and FLC both inhibit each other in a classical two gene mutual inhibition switch, a very similar model to that believed to control cell cycle progression. Such a switch is likely to have non-linear properties, and integrate day-length and temperature information in non-obvious ways to control the effects of weather, seasons, and climate on plant development.The first Objective, split into three parts, aims to discover missing components of the FT/FLC seasonal switch, and how the switch operates in response to seasonal combinations of temperature and photoperiod cues. We focus on the timing and duration of winter temperature cues, and how their sensing and efficacy can be modified by occurring in days with different photoperiods. For instance, temperature cues experienced in longer days might affect the system in a different way to temperature cues experienced in very short winter days.The second part of the proposal deals with identifying the tissue in which the switch occurs to control post-flowering reproductive development. We show striking preliminary evidence that the FT/FLC switch has a dramatic spatial dimension in flowers, with environmental cues and FT causing FLC mRNA expression to switch from the female organ to the male organ. We hypothesise therefore that environmental cues controlling seed dormancy are sensed in developing flower buds, also the time at which development of the first seed structures begins. This is interesting because it aligns our understanding of the behaviour of annual plants much more closely to perennial plants, in which buds are set in summer but are dormant until cold winter conditions break this dormancy and enable bud break in the spring. We will examine the effect of expressing FLC heterologously in the male and female flower organs on bud and seed development and dormancy, and aim to uncover the molecular mechanism that enables FLC expression to switch dramatically between the two flower organs in response to seasonal cues.