Systems analysis of tapetal regulatory networks required for pollen development

花粉发育是植物受精和种子形成的基础，对我们所吃的大部分食物的生产也是至关重要的。它在植物育种和杂交植物生产中也发挥着关键作用。杂交种(两个独立的植物品系杂交的结果)往往更有活力，与自交系相比，产量高出20%-30%。这一点有多么重要的一个例子是中国的杂交水稻，那里种植的杂交水稻品系每年为6000万人提供额外的食物。然而，混合动力车的生产既耗时又昂贵。我们越来越意识到人口的增加，以及对可持续、有效的农业系统的需求，这些农业系统的产量增加，但对环境的影响较小。了解花粉形成的过程是这类策略中至关重要的一步，因为它为选择性育种、最大限度地提高受精和杂交生产提供了机会。近年来，在理解花粉发育方面取得了重大进展，其中很大一部分来自于研究在模式植物拟南芥中无法产生可存活花粉(雄性不育)的突变体。然而，最近的进展意味着，有关拟南芥花粉调控网络的信息现在可以应用于作物。我们已经证明，拟南芥与水稻和大麦之间的花粉发育途径是高度保守的；因此，这些数据可以直接影响作物育种和杂交生产的策略。绒毡层是产生花粉最重要的花药组织之一，许多雄性不育突变体都表现出绒毡层异常。它在减数分裂、花粉壁形成和小孢子向花粉粒发育过程中起着关键的分泌作用。然而，人们对绒毡层和发育中的花粉之间的关系知之甚少，尽管绒毡层已被证明是必不可少的。败育小孢子(AMS)是绒毡层中的一个关键调控基因，在花粉发育过程中表现出长时间的表达，在花粉形成过程中具有多种作用，包括与减数分裂相关的早期事件和花粉壁物质合成和分泌的后期。我们对花粉壁形成过程中AMS的分析已经确定了AMS调控的靶标，包括参与花粉壁物质从绒毡层到花粉的运输的ABC转运蛋白，以及最近花粉壁的脂类生物合成。然而，它也参与早期的事件，例如减数分裂和绒毛膜程序性细胞死亡的进程。尽管我们有数据表明AMS监管着更多的目标，但还没有对这些其他角色的描述。在这项提案中，我们想要以我们现有的数据为基础，分析AMS在整个绒毛发育过程中的作用。我们还将使用可诱导的AMS结构来分析网络中关键组件的表达，并测试它们在花粉发育中的作用。我们将使用这一途径的数学模型来帮助理解该网络的细胞专一性，并确定该网络的组件，这些组件在绒毛膜和发育中的花粉之间的通信中发挥作用。我们还将确定AMS如何调节其靶标的表达，以及这是否通过改变染色质的状态来使其能够表达。这项工作将使我们更好地理解绒毡层和AMS调控网络如何控制花粉的形成。它将提供有关花粉发育的有价值的信息，这将有助于育种中的育性控制，以及为提高产量而开发杂交品系。在拟南芥中发现的调控网络在单子叶水稻和大麦中是保守的，因此对这些网络的比较分析将直接影响英国和世界各地的作物研究。

Pollen development is fundamental to plant fertilisation and seed formation, and is vital for the production of most of the food that we eat. It also plays a critical role in plant breeding and the production of hybrid plants. Hybrids (results of crossing two separate plant lines) tend to be more vigorous, with 20-30% higher yields, compared to self-fertilised lines. An example of how important this can be is seen with hybrid rice in China, where growing hybrid lines provides additional food for 60 million people/annum. However, the production of hybrids is both time-consuming and costly. We are becoming increasingly aware of population increases and the need for sustainable, effective agricultural systems, with increased yield but less environmental impact. Understanding the process of pollen formation is a vital step in such strategies since it provides an opportunity for selective breeding, maximising fertilization and hybrid production. Over recent years significant progress has been made towards understanding pollen development, much of this has come from studying mutants that fail to produce viable pollen (male steriles) in the model plant Arabidopsis. However recent advances, mean that information on pollen regulatory networks from Arabidopsis can now be applied to crops. We have shown that the pathways for pollen development between Arabidopsis and rice and barley are highly conserved; therefore such data can directly impact on strategies for crop breeding and hybrid production. One of the most important anther tissues for pollen production is the tapetum and many male sterile mutants show tapetal abnormalities. It plays a key secretory role in events associated with meiosis, pollen wall formation and in the development of microspores to pollen grains. However, little is known about the relationship between the tapetum and the developing pollen, although the tapetum has been shown to be essential. ABORTED MICROSPORE (AMS) is a key regulatory gene in the tapetum, which shows prolonged expressed during pollen development, which appears to have multiple roles during pollen formation, including early events associated with meiosis and later stages when synthesis and secretion of the pollen wall materials occurs. Our analysis of AMS during pollen wall formation has identified AMS regulated targets, including an ABC transporter, which is involved in the transport of pollen wall materials from the tapetum to the pollen and recently lipid biosynthesis for the pollen wall. However, it is also involved in earlier events, for example in the progression of meiosis and tapetal Programmed Cell Death. Although we have data that AMS regulates additional targets, there has been no characterisation of these other roles. In this proposal we want to build on our existing data and analyse the function of AMS throughout tapetal development. We will also analyse the expression of key components in the network using inducible AMS constructs and test them for their role in pollen development. We will use mathematical modelling of this pathway to help understand the cellular specificity of the network and determine components of the network, which are functioning in the communication between the tapetum and developing pollen. We will also determine how AMS regulates the expression of its targets and whether this is via a change in the status of the chromatin to make it accessible for expression. This work will provide a greater understanding of how the tapetum and the AMS regulatory network function to control pollen formation. It will provide valuable information about pollen development, which will be useful to facilitate control of fertility for breeding, and for the development of hybrid lines for increased yield. The regulatory networks found in Arabidopsis are conserved in the monocots rice and barley, thus the comparative analysis of these networks will directly impact onto crop research in the UK and worldwide.