Facing Forwards - Understanding epidermal development in cereals

As the primary source of calories, cereals are the cornerstone species of our food security. To sustainably meet food demands, we need to increase cereal grain yields without increasing inputs or using more land, all the while facing accelerating and more extreme temperature and drought events. Plants faced severe climate challenges millions of years ago when they expanded to living on land. To survive, land plants evolved a highly adaptive outer surface lined with epidermal cells that secrete a protective lipid-rich cuticle to prevent water loss and reflect incoming radiation, interspersed with adjustable air pores called stomata allowing plants to breathe and transpire. In this way, the outer epidermis balances protection and exchange with the above-ground environment. Fine-tuning this balance helps plants respond to changing and challenging environments. For example, grasses, including staple cereal crops develop extremely efficient stomatal complexes and thick waxy cuticles, key elaborations which help grasses save water and maintain temperature on hot, high light plains. Epidermal surfaces can also develop other types of specialised cells, including defensive structures such as hairs and silica-accumulating cells which can also influence epidermal water loss, cooling and stomatal function. We propose that these adaptive features of the cereal epidermis can be mobilised to engineer cereal crops which need less irrigation and maintain yield in future climates.
To do this, we need to understand how plants coordinate the cuticle and specialised cell types on the epidermis and the relevance of each component and their combinations to epidermal function. In a major advance in this effort, our research group recently revealed that deeply conserved, interacting genes control both epidermal cell patterning as well as cuticle properties in barley, thus identifying a shared upstream network controlling multiple epidermal features linked to cereal performance. This proposal exploits these findings as a platform to determine the crucial steps in epidermal development and how they influence each other, respond to environmental conditions and impact epidermal functions and whole plant productivity. We will deploy cutting edge approaches to profile cuticle and cell patterning in the epidermis at an unprecedented resolution and explore the interdepenc(ies) between these events. We will also exploit our genetic knowledge to evaluate genetic determinants in wheat, a closely related cereal which along with barley dominate temperate agriculture. Finally, we will use state-of-the-art controlled environments and specialist physiological methods to assess the impact of altered epidermal features on physiological function both at the tissue and whole plant level and future climate scenarios. Taken together, our research will deliver a step-change in our ability to design suites of epidermal features to future-proof our crops.

We aim to understand and exploit variation in epidermal features to future proof cereal crops from accelerating climate changes. To achieve this, we need to define the genes and developmental mechanisms controlling epidermal properties and how these contribute to physiological functions and whole plant performance. This proposal builds on our discovery of a coordinating genetic network controlling epidermal traits linked to plant performance and yield. These genes all promote wax deposition on the cuticle as well as formation and spacing of specialised epidermal cells such as stomata, epidermal hairs and silica cells, all features which help plants cope with stressful environments. We will use fine scale cuticular profiling coupled with single cell transcriptomic resolution to reconstruct pathways leading to different cell types and cuticular chemistries, followed by comparative analyses with mutant alleles in genes known to control specific features. We will also explore the interdependency between epidermal patterning decisions and cuticular properties using transgenic overexpression of cuticular enzymes. We will expand the epidermal genetic network through both forward and reverse approaches and by evaluating the function of orthologous genes in wheat. While advancing the power of our genetic tools to control epidermal patterning, we will deploy state of the art climate control and physiological sampling methods to reveal the impact of altered epidermal patterning on leaf physiology and function including stomatal conductance and intrinsic water use efficiency. These approaches will assess spatial and temporal control of epidermal patterning and the physiological impact of trait variation to identify desirable traits and ideotypes for crop production in future climates.