The shape of sustainable crop production - re-engineering plant architecture for sustainable food production

这个项目的重点是更好地描述重要作物物种植物地上部和根部重力反应背后的分子机制。这是为了改善作物结构，以改善光捕获，减少倒伏发生(芽)和/或养分获取和抗旱性(根)。这一领域的先前工作已经建立，侧根和芽通过在拟南芥模式生物中看到的向重力的设定点角度来保持其生长角度。向重力点角度是由其与重力向量的关系定义的角度，因此GSA为0的垂直向下的枝/根和植物器官保持在该GSA以响应向重力性(Digby，Fern，1995)。这种重力依赖的过程是由生长素植物激素介导的，生长素通量在上侧和下侧分别导致地上部和根部不同程度的伸长或伸长抑制。根/茎尖的重力感应器，根据淀粉-柱状石假说，双子叶和单子叶根的柱状细胞和双子叶茎的状态细胞是含有充满淀粉的淀粉质的极化细胞的集合，这些淀粉体通过淀粉沉积到细胞的特定极点来响应重力。当根/冠远离垂直方向时，由于淀粉向下沉积到细胞的新生底部区域，生长素向下流向茎/根的远轴方向的通量增加。这对生长素向茎和根的近轴侧的反重力偏移通量起到了相反的作用。器官近轴和远轴生长素浓度的差异导致细胞伸长不同，随后地上部向上弯曲，根部向下弯曲，返回到最初的GSA，以实现最佳植物生长(Roychoudhry和Kepinski，2021)。这种重力传感机制背后的分子过程已经在拟南芥模型中得到了很好的描述。例如，生长素转运蛋白PIN3、PIN4和PIN7的作用及其在建立地上部和根的重力性方面的作用(Roychoudhry等人，2022)。然而，对于许多重要的作物物种来说，将这种对根和地上部对重力的反应及其如何影响植物结构的理解转化为仍然是必要的，努力改善根系，以增加养分/水分的获取，以应对气候变化下日益普遍的干旱(以及在保持作物产量的同时减少植物茎折断的地上部倒伏)。利兹大学和其他地方的研究生研究员同事开展了对小麦和水稻等谷类物种的研究。小麦和水稻侧根都恢复到原来的GSA，小麦侧根恢复GSA的速度比水稻侧根快，这表明物种之间以及单子叶(谷类)和双子叶(拟南芥)之间的反应存在差异，水稻可能具有比小麦侧根更强的生长素依赖的反重力抵消反应。此外，调控根生长角度的水稻DRO1在缺水环境中过度表达时，随着更多垂直根系的发育而导致水稻产量增加(Walsh等人，未发表)。继续阐明作物品种根和地上部发育和维持的分子机制可以作为提高作物产量和建立更好的粮食安全的重要工具。一些作物，如大麦和高粱，已经建立了一些早期研究，而其他主要作物，如大豆，则没有。这一博士项目旨在扩大这些开创性作物物种的根部和地上部角度的知识，以设计出对日益恶化的气候变化问题具有适应能力的作物，重点是水稻和小麦等主要作物。

This project is focused on better characterising the molecular mechanisms behind gravitropic responses in plant shoots and roots for important crop species. This is for the purpose of engineering crop architecture to improving light capture and decrease lodging occurrence (shoots) and/or nutrient acquisition and drought tolerance (roots).Previous work in this field has established that lateral roots and shoots maintain their growth angles through gravitropic set-point angles as seen in arabidopsis model organisms. The gravitropic-set point angle is the angle defined by its relationship to the gravity vector so a vertically downward shoot/root possessing a GSA of 0 and plant organs are maintained at this GSA in response to gravitropism (Digby, Fern, 1995). This gravity-dependent process is mediated by auxin phytohormones with auxin flux on the upper and lower side leading to differential elongation or elongation inhibition in the shoots and roots respectively. The gravity-sensing apparatus of the root/shoot tip, according to the startch-statolith hypothesis, the columella of dicot and monocot roots and the statocytes of dicot shoots are a collection of polarised cells containing starch-filled amyloplasts which respond to gravity through starch sedimentation to a particular pole of the cell. As a consequence of downward starch sedimentation to the nascent bottom region of the cell when the root/shoot is moved away from the vertical, there is increased downward flux of auxin to the abaxial side of the shoot/root. This acts against the anti-gravitropic offset flux of auxin to the adaxial side of the shoot and root. This disparity between adaxial and abaxial auxin concentrations across the organ leads to differential cell elongation followed by the upward bending in shoots and downwards bending in roots to return to their initial GSAs for optimal plant growth (Roychoudhry and Kepinski 2021).The molecular process behind this gravity-sensing mechanism has been well characterised in arabidopsis models with work. For example, the role of the auxin transporters PIN3, 4 and 7 and their role in establishing gravicompetence in shoots and roots (Roychoudhry et al., 2022). However, translating this understanding of root and shoot responses to gravity and how that impacts plant architecture is still necessary for numerous important crop species, with efforts aimed at improving rooting for increase nutrient/water acquisition in response to increasing drought prevalence under climate change (as well as decreasing shoot lodging where the plant stem snaps whilst maintaining crop yield).Work into cereal species such as wheat and rice has been conducted by fellow postgraduate researchers at the University of Leeds, and elsewhere, with both wheat and rice lateral roots returning to their original GSAs with wheat laterals restoring their GSAs faster than rice laterals which shows variation in the response between species as well as monocots (cereals) and dicots (arabidopsis) with rice potentially possessing a stronger auxin-dependent anti-gravitropic offset response relative to wheat lateral roots. Additionally, rice DRO1 which regulates root growth angle has shown to lead to higher rice yields in water-scarce environments when overexpressed as more vertical root systems are developed (Walsh et al., unpublished). Continuing to elucidate the molecular mechanisms of root and shoot angle development and maintenance in crop species can act as a crucial tool in improving crop yields and establishing better food security. Some crops such as Barley and Sorghum have some early research established whilst other staple crops like soybean have none. This PhD project aims to expand the knowledge of root and shoot angles in these seminal crop species to engineer crops that are resilient to the ever worsening issues of climate change with key emphasis on staple crops like rice and wheat.