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

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.