Dynamics and evolution of a halogenated auxin - a seed-derived signal for pea pod growth

在地球生命史上，开花植物（被子植物）的进化可以说是塑造当今世界的最具影响力的事件之一。超过95%的现存植物属于被子植物门，驯化的开花植物是人类食物中蛋白质和能量的重要来源。被子植物成功的一个主要原因是在花的中心形成心皮，在授粉后形成果实，为下一代保存种子。拟议的研究利用了一种新型激素变异的动态和进化及其在代际信号传导中的作用的最新进展。豌豆（Pisum sativum）是一种具有广泛遗传学研究历史的作物植物，也是豆科作物的有用模型。与模式植物拟南芥（Arabidopsis thaliana）不同，拟南芥产生双心果（双室）和许多小种子，豌豆产生单心果（单室），果实（或豆荚）相对较大，但种子较少。因此，破译调节豌豆生殖发育的种子/豆荚分子对话可能会导致发现替代信号系统。此外，鉴于豆科作物在提供植物性蛋白质和实现低投入农业方面的重要作用，改进豆科作物具有广泛的环境和健康影响。生长素是一种多功能激素，几乎在植物发育的各个方面发挥作用，包括果实形成。豌豆（以及豆科的豆科和三叶草科（F/T）部落中的其他物种）产生一种氯化的生长素变体，4-Cl-IAA，在果实和种子中丰富。豌豆幼荚去籽后，豆荚的进一步生长很少或没有，外源IAA的施用对这一点没有影响。相比之下，外源施用4-Cl-IAA促进生长，导致结籽豆荚完全伸长。因此，4-Cl-IAA可能履行了受精胚珠/种子通常在刺激果实生长中发挥的作用，通过提供种子到荚果的移动信号来传达受精已经发生。在本文中，我们将阐明这种生长素变异的合成、信号传导和进化，揭示一种新的信号通路的形成。鉴于拟议工作的重大战略潜力，影响目标旨在利用所获得的知识来推进豆科农学并探索医疗行业药物开发的潜力。本研究将从信号多样化的分子机制出发，探讨4-Cl-IAA的生物合成和信号传导对豆科F/T部落生殖器官生长的影响。除了对现有激素的修饰如何产生新的生长信号的基本理解之外，这个项目的结果具有直接影响作物改良和药物发现等学科的潜力。

In the history of life on Earth, the evolution of flowering plants (angiosperms) is arguably one of the most impactful events that has shaped the world of today. More than 95% of extant plants belong to the angiosperm phylum and domesticated flowering plants are essential sources of protein and energy in food consumed by humans. A major reason for the success of angiosperms is the formation of carpels in the centre of the flowers that develop as fruits after pollination harbouring the seeds for the next generation. The proposed research capitalises on recent advances into the dynamics and evolution of a novel hormone variant and its role in inter-generational signalling. Pea (Pisum sativum) is a crop plant species with an extensive history in genetics research, and a useful model for legume crops in general. In contrast to the model plant Arabidopsis thaliana, which produces bicarpellate (two-chambered) fruit with many small seeds, pea produces monocarpellate (single-chambered) fruit (or pods) with comparatively larger but fewer seeds. Deciphering the seed/pod molecular conversation that regulates pea reproductive development may therefore lead to the discovery of alternative signalling systems. Moreover, given the important role of legume crops in the provision of plant-based protein and in achieving low-input agriculture, the improvement of legume crops has wide environmental and health implications. Auxin is a versatile hormone functioning in practically all aspects of plant development, including fruit formation. Pea (along with other species in the Fabeae and Trifolieae (F/T) tribes of the legume family) produces a chlorinated variant of auxin, 4-Cl-IAA, which is enriched in fruit and seed. Deseeding a young pea pod leads to little or no further growth of the pod and application of exogenous IAA has no effect on this. In contrast, exogenously applied 4-Cl-IAA promotes growth leading to full elongation of the deseeded pods. 4-Cl-IAA may therefore fulfil the role that fertilised ovules/seeds ordinarily play in stimulating fruit growth by providing a mobile seed-to-pod signal to communicate that fertilisation has taken place. In this proposal, we will elucidate synthesis, signalling and evolution of this auxin variant revealing the formation of a novel signalling pathway. Given the significant strategic potential of the proposed work, the impact objectives aim to exploit the obtained knowledge to advance legume agronomy and explore potential for drug development in the medical industry. With a focus on the molecular mechanism of signal diversification, the proposal will investigate the impact of 4-Cl-IAA biosynthesis and signalling on reproductive organ growth in the F/T tribes of the legume family. Over and above the fundamental understanding of how modification of an existing hormone can generate a novel signal for growth, results from this project have immediate potential to impact disciplines as far apart as crop improvement and drug discovery.