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

在地球生命的历史上，开花植物(被子植物)的进化可以说是塑造了当今世界的最具影响力的事件之一。现存的95%以上的植物属于被子植物门，驯化的开花植物是人类消费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，花在授粉后发育为果实，为下一代提供种子。这项拟议的研究利用了一种新的激素变体的动力学和进化及其在代际信号传递中的作用的最新进展。豌豆(Pisum Sativum)是一种具有广泛遗传研究历史的农作物，也是豆科作物的有用模式。与模式植物拟南芥不同，拟南芥产生具有许多小种子的双果(两室)果实，而豌豆产生具有相对较大但较少种子的单果(或单室)果(或豆荚)。因此，破译调控豌豆生殖发育的种子/豆荚分子对话可能会导致发现替代的信号系统。此外，鉴于豆类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，豆类作物的改良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，包括果实的形成。豌豆(以及豆科豆科和三叶族(F/T)部落的其他物种)产生一种生长素的氯化变体4-氯-IAA，它富含果实和种子。豌豆幼荚脱粒后，幼荚几乎不再生长，外源IAA的应用对此没有影响。相反，外源4-氯-IAA促进了去籽豆荚的生长，使其完全伸长。因此，4-氯-IAA可以发挥受精胚珠/种子通常在刺激果实生长方面的作用，提供一种从种子到豆荚的移动信号，传达受精已经发生的信息。在这个提案中，我们将阐明这种生长素变体的合成、信号传递和进化，揭示了一种新的信号通路的形成。鉴于拟议工作的巨大战略潜力，影响目标旨在利用所获得的知识来促进豆类农艺并探索医疗行业药物开发的潜力。该提案将重点放在信号多样化的分子机制上，研究4-氯-IAA的生物合成和信号对豆科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，该项目的结果还有可能立即影响到远离作物改良和药物发现的学科。

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.