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

该项目的重点是更好地表征重要作物品种植物芽和根向重力反应背后的分子机制。这是为了工程改造作物结构，以改善光捕获并减少倒伏发生（芽）和/或养分获取和耐旱性（根）。该领域的先前工作已经确定侧根和芽通过向重力设定点保持其生长角度正如在拟南芥模式生物中所见。向重力性设定点角度是由其与重力矢量的关系定义的角度，因此具有GSA为0的垂直向下的茎/根和植物器官响应向重力性而保持在该GSA（迪格比，Fern，1995）。这种重力依赖的过程是由生长素植物激素介导的，生长素流量在上部和下部，分别导致芽和根的差异伸长或伸长抑制。根/茎尖的重力感应装置，根据startch-statolith假说，双子叶植物和单子叶植物根的柱和双子叶植物茎的平衡细胞是一个极化细胞的集合，含有淀粉填充的造粉体，其通过淀粉沉积到细胞的特定极来响应重力。由于向下的淀粉沉降到初生的底部区域的细胞时，根/芽是远离垂直移动，有增加的向下通量的生长素的茎/根的远轴侧。这对生长素的反重力偏移通量的近轴侧的芽和根。整个器官的近轴和远轴生长素浓度之间的这种差异导致细胞差异伸长，然后是芽的向上弯曲和根的向下弯曲，以返回到其初始GSA以实现最佳植物生长（Roychoudhry和Kepinski 2021）。例如，生长素转运蛋白PIN 3、4和7的作用及其在芽和根中建立重力感受性的作用（Roychoudhry et al.，2022年）。然而，将这种对根和芽对重力的反应以及这种反应如何影响植物结构的理解转化为许多重要的作物物种仍然是必要的，为应对气候变化下日益严重的干旱，（以及减少植物茎折断的枝条倒伏，同时保持作物产量）利兹大学和其他地方的研究生研究人员已经对小麦和水稻等谷物物种进行了研究，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，这表明小麦侧根和水稻侧根的GSA之间存在差异。物种之间的反应以及单子叶植物（谷物）和双子叶植物（拟南芥）与水稻可能拥有一个更强的生长素依赖性的反重力抵消反应相对于小麦侧根。此外，调节根生长角度的水稻DRO 1已显示当过表达时在缺水环境中导致更高的水稻产量，因为发育了更多的垂直根系（沃尔什等人，未出版）。继续阐明作物物种根和茎角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有一些早期的研究，而其他主要作物如大豆没有。这个博士项目旨在扩大这些种子作物物种的根和芽角度的知识，以工程作物适应日益恶化的气候变化问题，重点是水稻和小麦等主食作物。

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.