Diving Deeper: Unravelling How Plants Regulate Root Growth Angle

有限的水和养分供应是全球作物生产和粮食安全的主要制约因素。考虑到气候变化对水资源供应的影响以及减少化肥投入以使农业在环境上更具可持续性的推动，这些制约因素正在随着时间的推移而加剧。因此，开发养分和水分捕获效率更高的作物可以为显著提高作物的抗逆性和产量提供解决方案，以满足日益增长的世界人口对粮食的需求。在这种情况下，根角是一种很有前途的根系结构特征，因为它对不同土壤剖面的养分和水分捕获有重要影响。例如，较陡的根角可以从较深的土壤中获得流动的水和氮，而较浅的根角则可以从表土中捕获不流动的磷。作物根系包括不同类型的根（如初生根、种子根、侧根和冠根），它们以不同的角度生长，以有效地从不同的土壤剖面获取资源。这些不同的根角是由地向偏移和反地向偏移（AGO）机制决定的。以往的研究已经发现了许多与向地性反应机制有关的基因，但对AGO机制的了解有限。为了弥补这一空白，我们最近发现了一个参与AGO机制的新基因（称为增强向重力性1，即EGT1）。该基因的突变导致所有根类型只能垂直向下生长，因为它阻碍了它们保持不同生长角度的能力。我们的研究进一步发现突变根主要在两个生物过程中存在缺陷，即活性氧（ROS）维持和细胞壁刚度。由于已知根中的ROS水平决定细胞壁的刚度或松动，我们提出了一种新的AGO机制，即EGT1基因通过调控ROS依赖的细胞壁刚度来控制不同根类型的根角（Fusi et al., 2022）。PNAS)。在这项BBSRC新研究者资助中，我们将研究大麦根中提出的AGO机制，以确定它如何允许不同类型的根生长并有效地从不同的土壤剖面中捕获水分和养分。我们将首先确定EGT1基因在根（特定组织和生长区）的何处转录，以及蛋白质的制造和积累。然后，我们将在EGT1突变体的这些组织和区域（称为互补）中特异性表达EGT1，以确认EGT1功能主要需要的组织和区域。接下来，我们将确定EGT1如何控制涉及ROS和细胞壁刚度过程的下游靶标。最后，我们将在水、营养和高温胁迫条件下培养野生型、突变型和组织区特异性互补系，以了解植物如何利用AGO机制来改变根角以应对这些条件。我们还将揭示突变型与野生型的角度变化是否能更好地在这些非生物胁迫条件下生长。本研究中获得的知识将为EGT1及其关键下游靶点提供重要的新信息，这些靶点涉及AGO机制和控制根角以响应环境线索。这将有助于育种者设计新的方法来加强资源捕获和提高作物产量，支持改善英国和全世界粮食安全的努力。因此，我们项目的职权范围属于BBSRC可持续农业和食品生物科学支持的战略优先领域。

Limited water and nutrient availability are the major constraints for global crop production and food security. These constraints are intensifying over time given the impact of climate change on water availability and the drive to reduce fertiliser inputs to make agriculture more environmentally sustainable. Therefore, developing crops with improved nutrient and water capture efficiency could provide the solution to make significant improvements in stress resilience and yields in our crops to meet the food demand of an increasing world population. In this context, root angle is a promising root architectural trait as it critically influences nutrient and water capture from different soil profiles. For instance, steeper root angle accesses mobile water and nitrogen from deeper soils, while shallow root angle improves capture of immobile phosphorous from topsoil. Crop root systems include different root types (such as primary, seminal, lateral and crown), which grow at different angles to efficiently capture resources from different soil profiles. These different root angles are determined by gravitropic and anti-gravitropic offset (AGO) mechanisms. Previous research has uncovered many genes involved in gravitropic response machinery, however such knowledge about AGO mechanism is limited. To bridge this gap, we recently identified a novel gene (called Enhanced Gravitropism 1 i.e., EGT1) involved in AGO mechanism. A mutation within this gene causes all root types to grow only vertically downwards as it hinders their ability to maintain different growth angles. Our research further identified that mutant roots are defective in mainly two biological processes called as reactive oxygen species (ROS) maintenance and cell wall stiffness. As ROS levels in the root are known to determine cell wall's stiffness or looseness, we proposed a new AGO mechanism that EGT1 gene regulates ROS dependant cell wall stiffness to control root angle in different root types (Fusi et al., 2022. PNAS). In this BBSRC New Investigator grant we will investigate the proposed AGO mechanism in barley roots to determine how it allows different root types to grow and capture water and nutrients efficiently from different soil profiles. We will first determine where in the root (specific tissues and growth zones) EGT1 gene is transcribed and the protein is made and accumulates. We will then express EGT1 specifically in these tissues and zones in the egt1 mutant (called complementation) to confirm tissue and zone predominantly required for EGT1 function. Next, we will determine how EGT1 controls downstream targets involved in ROS and cell wall stiffness processes. Finally, we will grow the wildtype, mutant and tissue and zone-specific complementation lines under water, nutrient and high temperature stress conditions to understand how this AGO mechanism is used by plant to change root angle in response to these conditions. We will also uncover whether change in angle in the mutant vs wildtype and complementation line roots are better able to grow under these abiotic stress conditions.The knowledge gained in this study will provide vital new information about EGT1 and its key downstream targets involved in AGO mechanism and controlling root angle in response to environmental cues. This will help breeders to design novel approaches to enhance resource capture and improve yield in crops, supporting efforts to improve food security in the UK and worldwide. The remit of our project thus falls under a strategic priority area supported by the BBSRC Bioscience for Sustainable Agriculture and Food.