Biomechanics and architecture of developing plant organs

植物不断受到来自风、大雪甚至自身重量的机械挑战。在木材中，机械阻力来自死细胞的木质化残留物。相比之下，芽和根需要保持它们的细胞存活，并在寻找光线或营养的过程中快速生长。因此，年轻的植物器官必须使用智能机械策略来保持直立，例如在发芽期间穿过坚硬的土壤时，同时保持灵活和动态。已经确定了一些对器官生长和姿势至关重要的基因，但基因只能通过在细胞水平上控制生物化学来起作用。我们仍然不知道器官行为是如何从单个植物细胞之间的相互作用中产生的。在这个项目中，我提出通过结合植物幼体器官的工程和生物学观点来填补基因表达和器官力学之间的空白。根和茎组织高度组织成不同细胞大小和形状的层，让人想起复合材料。这导致了这样一种想法，即细胞和组织层的结构和排列，即器官解剖，可能是自然选择的，以优化关键的生物功能，如根生长或茎对机械负荷的响应能力。我提出了一种多学科的方法来探索植物在保持其力量和感知外力的能力的同时快速生长的机械策略。结合生物实验和建模，解剖植物器官在生长过程中不同层次的组织。我的团队将开发新的方法来量化不同尺度的机械性能，从单个细胞到组织和器官。使用先进的显微镜技术，我们将研究在器官水平上施加的外力是如何在组织和细胞水平上转化的。然后，单细胞和组织水平的实验数据将被整合到基于物理的植物器官生长的3D模拟中。这样的计算模型将帮助我们了解哪些因素，从细胞弹性到解剖特征，控制整个器官的机械性能和生长。除了发展研究之外，这种知识还可以为解决农业问题——例如作物在致密土壤中倒伏和发芽——提供关键，并有助于开发适应气候变化的新育种方法。

Plants are constantly challenged mechanically, by wind, heavy snow falls or even their own weight. In wood, mechanical resistance comes from lignified remains of dead cells. In contrast, shoots and roots need to keep their cells alive and grow quickly in search of light or nutrients. Young plant organs have therefore to use smart mechanical strategies to stay straight, e.g. when pushing through hard soil during germination, while remaining flexible and dynamic. Some of the genes essential for organ growth and posture have been identified, but genes can only act via controlling biochemistry at the cellular level. We still don't know how organ behavior emerges from the interactions between individual plant cells. In this project I propose to fill the gap between gene expression and organ mechanics by combining engineering and biological viewpoints on young plant organs. Root and stem tissues are highly organized into layers of different cell size and shape, reminding of composite materials. This leads to the idea that the structure and arrangement of cells and tissue layers, i.e. organ anatomy, could have been naturally selected to optimize key biological functions such as root growth or the ability of stems to respond to mechanical loads. I propose a multi-disciplinary approach to explore the mechanical strategies used by plants to grow fast while maintaining their strength and ability to sense external forces. Combining biological experiments and modelling, I will dissect the different levels of organization of plant organs during growth. My group will develop new methods to quantify mechanical properties at different scales, from single cells to tissues and organs. Using advanced microscopy techniques, we will investigate how external forces applied at the organ level are translated at the levels of tissues and cells. Experimental data at the single cell and tissue level will be then integrated into a physically-based 3D simulations of growing plant organs. Such computational models will help us understand which factors, from cell elasticity to anatomical features, control mechanical performance and growth of the whole organ. Beyond developmental research, this knowledge can provide keys to address agricultural issues - such as crop lodging and germination in compact soils - and contribute to developing new breeding practices for a changing climate.