Signalling Sex in Plants: The Role of Peptide Signals and the Cell Wall in Fertilisation

植物繁殖是种子生产的基础，也是粮食安全的核心，然而我们对胚珠（雌性配子）与花粉（雄性配子）受精的分子过程的理解仍然不完整。受精涉及到配子之间严格调节的交流，以确保花粉管到达胚珠，并在胚珠内的正确位置释放精细胞。这种分子对话的核心是一组相关的受体激酶，它们跨越细胞膜来检测细胞外的小分子。这些受体的信号检测通过不同的下游事件转化为适当的细胞反应。我们知道这个受体家族结合小蛋白（多肽）作为外部细胞信号，但是在花粉管接收过程中在花粉管和胚珠之间传递的多肽的身份尚不清楚。下游事件可能包括细胞壁组成的变化，使胚珠入口处的一个专门的协同细胞退化，以及胚珠内花粉管的破裂，但支持这一观点的功能数据有限，细胞壁变化的范围尚不清楚。因此，人们对花粉管接收过程中的肽受体细胞壁信号传导知之甚少。我们将在本项目中利用拟南芥解决一些关于花粉管到胚珠的信号传导问题：1)胚珠上的三种受体激酶能感知哪些肽？2)受精过程中哪些胚珠细胞壁成分的变化是重要的，哪些受体介导了这些变化？3)相似的肽信号是否从胚珠传回花粉管；4)它们是否也会导致受精所需的细胞壁成分变化？这些问题直接导致了项目的目标。首先，我们将对活胚珠中的受体信号进行分析，并测试对一组合成胚珠和花粉管肽的反应，以确定哪些肽和受体相互作用。其次，我们将绘制正常植物和缺乏关键胚珠受体的突变体在花粉管接受过程中胚珠细胞孔组成的图谱。遗传和生化技术将用于测试多肽与胚珠受体相互作用的功能意义，以及细胞壁变化对受精的重要性。第三，我们将测试类似的肽是否从胚珠传回到花粉管受体，第四，受精过程中花粉管细胞壁的组成发生了什么变化，随后对这些功能进行遗传和生化表征。因此，我们将在理解植物受精的基本过程方面取得重大进展，将信号转导与细胞壁组成改变联系起来，并为信号传导如何控制配子反应提供新的见解。从长远来看，农业将受益于对植物施肥机制的更深入了解，这一过程对我们所有主要作物都很重要。由于这一基本过程的进化保守性，了解模式植物中受精是如何发生的，可以为提高作物的受精（和产量）提供信息。这在当前气候紧急情况的背景下尤为重要，因为越来越多的极端温度事件影响了施肥，从而影响了产量。所获得的知识将有助于培育适应气候变化的作物。这个项目的受益者包括科学界，他们将从扩大对植物信号的理解中获益，利用施肥作为一个可处理的模型系统。博士后研究助理和技术人员将受益于遗传学、生物化学、分子生物学、发育生物学和细胞生物学的培训。最后，通过支持与瑞士的合作，该项目将加强国际联系。

Plant reproduction underpins seed production and is central to food security, yet our understanding of the molecular process by which ovules (the female gametes) are fertilised by pollen (the male gametes) remains incomplete. Fertilisation involves tightly regulated communication between the gametes to ensure that the pollen tube reaches the ovule and releases the sperm cells at the correct position within the ovule. At the core of this molecular conversation is a group of related receptor kinases which span the cell membrane to detect small molecules outside the cell. Signal detection by these receptors is translated into an appropriate cell response via varied downstream events. We know that this family of receptors binds small proteins (peptides) as external cell signals, however the identity of the peptides that pass between the pollen tube and ovules during pollen tube reception is unknown. Downstream events likely include changes in cell wall composition to allow degeneration of a specialised synergid cell at the entrance of the ovule, and burst of the pollen tube within the ovule, but functional data to support this idea is limited, and the range of cell wall changes unclear.Peptide-receptor-cell wall signalling during pollen tube reception is, thus, poorly understood. We will address a number of questions regarding signalling from the pollen tube to the ovule and vice versa in this project using Arabidopsis: 1) which peptides are perceived by the three receptor kinases at the ovule?; 2) which ovule cell wall composition changes during fertilisation are important and which receptors mediate these changes?; 3) are similar peptide signals passed back to the pollen tube from the ovule?; and 4) do they also result in cell wall composition changes required for fertilisation? These questions lead directly to the objectives of the project.Firstly, we will use an assay for receptor signalling in living ovules and test responses to a panel of synthesised ovule and pollen tube peptides to identify which peptides and receptors interact. Secondly, we will produce an atlas of cell well composition in ovules during pollen tube reception in normal plants and mutants lacking the key ovule receptors. Genetic and biochemical techniques will be used to test the functional significance of the interaction of peptides with the ovule receptors, and importance of the cell wall changes for fertilisation. Thirdly, we will then test if similar peptides signal from the ovule back to pollen tube receptors, and fourthly, what changes are seen in pollen tube cell wall composition during fertilisation, following up with genetic and biochemical characterisation of these functions. We will therefore make a significant advance in our understanding of the fundamental process of plant fertilisation, linking signal transduction to altered cell wall composition, and providing novel insight into how signalling controls gamete responses.Longer term, the agricultural industry will benefit from greater understanding of the mechanism behind plant fertilisation, a process important for all our major crops. Due to evolutionary conservation of this fundamental process, knowledge of how fertilisation occurs in a model plant can inform attempts to improve fertilisation (and yield) in crops. This is particularly relevant in the context of the ongoing climate emergency, with more extreme temperature events affecting fertilisation and thus yield. The knowledge gained will contribute to efforts to breed climate ready crops. Beneficiaries of this project include the scientific community who will gain from expanded understanding of plant signalling, using fertilisation as a tractable model system. A post-doctoral research associate and technician will benefit from training in genetics, biochemistry, and molecular, developmental and cell biology. Finally, by supporting a collaboration with Switzerland, the project will strengthen international ties.