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

植物利用季节信号、温度和日长来计时它们从营养发育到生殖发育的转变。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高度研究的领域，从中出现了一个简单的范例，特别是在控制开花时间方面。首先，长期温度是通过FLC基因座来感知的，已知温度会影响FLC基因的转录(至少部分通过反义转录调控)，并导致FLC的表观遗传变化，反映季节性进展。在叶子中，FLC抑制了第二个关键基因FT的表达，该基因在其启动子上接收到一个单独的信号，反映了一天的长度。因此，温度和日长信息被认为在FT启动子中起附加作用，以改变植物的行为。FT是一种一般的韧皮部移动的季节性信号，在目标细胞中作为转录辅助因子来促进与夏季相关的发育程序。我们一直在研究控制种子休眠的相同的季节性感知途径。这是一个母性过程，通过这个过程，母亲利用她对季节信息的记忆来影响其后代种子的休眠特征。通过这种方式，我们以前已经证明，季节信息在植物中从母亲传给后代。我们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启动子上季节性提示的逐步相加整合的范例不能解释我们对种子休眠的母性控制的观察。具体地说，我们利用遗传学、基因表达分析和染色质免疫沉淀证明了FLC是以前未被识别的FT的直接靶标，并且FT可以向反义FLC启动子传递全天信息。因此，我们提出了一个新的植物季节感知模型，在该模型中，FT和FLC都在经典的双基因相互抑制开关中相互抑制，这一模型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、季节和气候对植物生长的影响。第一个目标分为三个部分，旨在发现FT/FLC季节开关中缺失的部分，以及该开关如何响应温度和光周期信号的季节性组合。我们专注于冬季温度信号的时间和持续时间，以及如何通过在不同光周期的日子发生来改变它们的感知和有效性。例如，在较长的白天经历的温度信号可能会以不同于在非常短的冬季白天经历的温度信号的方式影响系统。提案的第二部分涉及识别发生转换的组织，以控制开花后的生殖发育。我们的初步证据表明，FT/FLC开关在花中具有戏剧性的空间维度，环境线索和FT导致FLC mRNA的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是在花芽发育中感觉到的，也是第一批种子结构开始发育的时间。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更接近，多年生植物的花蕾在夏季萌发，但在寒冷的冬季条件打破休眠并在春季萌芽之前一直处于休眠状态。我们将研究FLC在雄花和雌花器官中异源表达对芽和种子发育和休眠的影响，并旨在揭示使FLC表达在两个花器官之间显著切换的分子机制。

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.