Controlled buckling as a mechanism to regulate cuticle patterning in plants

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The outer surfaces of plants are covered in a thin layer of a water-repellent material called the cuticle. The cuticle protects the plant from dehydration when the air is dry, and it also protects the plant's delicate tissues from damage by insects and other animals and from invasion by pathogens such as bacteria and fungi. Having a cuticle is absolutely essential for the survival of all plants on land, and the evolution of the cuticle was a key step when plant life first moved onto the land, having begun in the sea.We are interested in the patterns that we find on the surface of plant cuticles. These patterns are formed from ridges, wrinkles or waves in the cuticular material. They can appear random, or can follow very organised arrangements such as sets of long lines or star shapes. They may also be absent, giving an entirely smooth cuticle. All of these different cuticle patterns affect the way that the plant interacts with the world around it, depending on the type of pattern and the organ on which it forms. For example, long ridges on the petal cuticle, if organised in a regular way, can interfere with light arriving at the plant surface and produce iridescent effects. These can be important on flowers to attract pollinators. A different example is the larger scale ridges found on some leaves, which make the leaf surface slippery for insects that grip with adhesive pads on their feet. As a result, these plants are protected from some of the beetles that would otherwise eat them. Cuticle patterns can also affect the wettability of the plant surface, and one of the least wettable plants, the Sacred Lotus, has provided the inspiration for the design of paints and other surface coatings that shed water (widely known as the "Lotus effect").Nobody knows how these different patterns form on the plant surface, but our preliminary data suggest that they are produced by buckling of the cuticular material as the plant cells grow. We have developed a model which suggests that buckling forces arise because the plant cells grow more in one direction than another, and this stretches and compresses the cuticle on top. Our model suggests that buckling can only occur if the cuticle is of the right stiffness, which will be a result of the detailed chemical make-up of the cuticle. The model suggests that we can think of the patterns on the plant surface as a result of the emergent properties of the plant cells and their cuticle - if cell growth, cuticle chemistry and cuticle production come together in a specific way, then buckling will occur and patterns will be formed.In this proposal we would like to test our model, to gain a detailed understanding of how cuticle patterns form. We believe that this understanding will be important in a range of ways, providing inspiration for the production of artificial surfaces with different roles, suggesting ways of improving crop yield by manipulating the plant's interaction with the environment, and even providing input into biodiversity and conservation work by explaining how plants interact with their environments in more detail. To test our model we will use a range of different approaches to change or perturb the growth of plant cells, the amount of cuticle produced, and the chemistry of cuticle. We will then analyse how these changes influence cuticle buckling and pattern formation. Many of our approaches will rely on altering the activity of the genes controlling cell growth and cuticle production or chemistry, but we will also use physical stretching of plant tissues and pharmacological (chemical) disruption of cell growth to give a wide range of different cuticle patterns. Our data will feed back into our model and provide a strong understanding of this important biological process.