Root SAT-NAV: uncovering the molecular mechanisms guiding root angle in soil

粮食安全是一个重大的全球问题。到2050年，作物产量必须翻一番，才能跟上全球人口增长到90亿的步伐。考虑到气候变化对水供应的影响以及减少化肥投入以使农业更具环境可持续性的目标，这一目标更具挑战性。在这两种情况下，开发具有更高的水和养分吸收效率的作物将大大有助于解决问题。根构型严重影响养分和水分的吸收效率。例如，可以通过操纵根系生长角度来更好地探索其积累的表土来显着提高磷的吸收效率。尽管有这些知识，但调节作物根角的基因仍有待确定。根角主要受向重力反应的调节。然而，其他方向性信号，如水分梯度诱导根系的应力激活向性导航（SAT-NAV）系统时，遇到干燥的土壤。尽管它们的重要性显而易见，但目前尚不清楚向水性如何与向重力性相互作用，使根能够觅食水。因此，了解根角的遗传和环境调节对作物改良至关重要。我们最近与合作者一起证明，根尖通过形成植物激素生长素和ABA的梯度来响应重力或水分的变化。在重力刺激后，生长素积累在根的下侧，抑制细胞生长并导致根在重力方向上弯曲。我们怀疑ABA以类似的方式指导根向水生长。这些激素是如何引起这些变化的？我们已经确定了约570个基因，生长素调节引起根弯曲。因此，生长素对根弯曲的影响非常复杂。为了帮助我们处理这种复杂性，我们将采用一种新的方法，称为系统生物学，它汇集了生物学和数学的精华。这涉及到生成大量关于这些不同基因及其控制过程的实验信息，然后将其整合到数学模型中。生长素通过诱导许多不同细胞和组织的反应来调节根弯曲。因此，我们的模型不仅要包括一系列基因的信息，还要考虑它们在许多不同的根细胞和组织中的行为。然后，我们需要通过设计实验来测试根模型准确预测真实的结果的能力，从而确定根模型的现实程度。然后，该模型可以用于测试想法，并提供关于生长素（或ABA）如何在基因，细胞和组织水平上控制根弯曲的新见解。测试我们在实验室中的发现是否与土壤相关将非常重要。我们将通过利用非侵入性成像的新进展来解决这一重要问题，以利用X射线显微计算机断层扫描（CT）来监测土壤中的根系生长。利用这种新的成像能力，我们将测试改变水稻根系向重力性和向水性对根系水分和养分吸收效率的影响。从这项研究中获得的知识将有助于科学家了解如何最好地操纵根角和提高作物产量。

Food security represents a major global issue. Crop production has to double by 2050 to keep pace with global population increasing to 9 billion. This target is even more challenging given the impact of climate change on water availability and the aim to reduce fertilizer inputs to make agriculture become more environmentally sustainable. In both cases, developing crops with improved water and nutrient uptake efficiency would contribute significantly to the solution. Root architecture critically influences nutrient and water uptake efficiency. For example, phosphate uptake efficiency could be significantly improved by manipulating root growth angle to better explore the topsoil where it accumulates. Despite this knowledge, the genes that regulate root angle in crops remain to be identified. Root angle is primarily regulated by the gravitropic response. However, other directional signals like water gradients induce roots' stress-activated-tropisms navigation (SAT-NAV) system when encountering drying soil. Despite their obvious importance, it is currently unclear how hydrotropism interacts with gravitropism to enable roots to forage for water. Understanding the genetic and environmental regulation of root angle is therefore of vital importance to crop improvement.Together with our collaborators, we have recently shown that root tips respond to changes in gravity or moisture by forming gradients of the plant hormones, auxin and ABA, respectively. After a gravity stimulus, auxin accumulates on the lower side of roots, inhibiting cell growth and causing roots to bend in the direction of gravity. We suspect that ABA functions in a similar way to direct root growth towards water. How do these hormones cause these changes? We have identified ~570 genes that auxin regulates to cause root bending. The effect of auxin on root bending is therefore very complicated. To help us deal with this complexity, we will employ a new approach termed Systems Biology that brings together the best of Biology and Maths. This involves generating a large body of experimental information about these different genes and the processes they control that is then integrated into mathematical models. Auxin regulates root bending by inducing responses in many different cells and tissues. Our model therefore has to include information not just about a list of genes but also consider their behaviour in many different root cells and tissues. We then need to determine how realistic our root model is, by designing experiments to test its ability to accurately predict real results. The model can then be used to test ideas and provide new insight about how auxin (or ABA) controls root bending at the gene, cell and tissue level. It will be very important to test whether our findings in the lab are relevant to soil. We will address this important question by exploiting new advances in non-invasive imaging to monitor root growth in soils using X-ray micro Computed Tomography (CT). Using this new imaging capability we will test the impact of altering root gravitropism and hydrotropism on root water and nutrient uptake efficiency in rice. The knowledge gained from this study will help scientists understand how best to manipulate root angle and enhance crop yield.