Student Speaker

The Glossy2 and Glossy2-like Genes Play Important Roles in Cuticle Structure and Function on Maize Silks

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Abstract

Climate change has increased the incidence of extreme weather events such as drought and heat that negatively impact crop health and productivity. A plant’s primary defense against water loss in the face of these hardships is its cuticle, a waxy layer produced and secreted by the epidermis of aerial organs. The cuticle acts as an external barrier to the environment, including as a barrier to water loss. The cuticle is comprised of a variety of very long chain fatty acids and their derivatives, such as hydrocarbons, alcohols, aldehydes, ketones, and wax esters. Classical genetic strategies have identified numerous glossy genes, only some of whose functions have been characterized. We have focused on the functional characterization of the maize Glossy2 (Gl2) gene and its ortholog, Glossy2-like, which share 63% amino acid similarity. Gl2 is primarily expressed in seedlings, immature leaves, and silks, whereas Gl2-like is primarily expressed in silks. In this study, we extracted and characterized cuticular waxes via gas chromatography-mass spectrometry from leaves and silks of wildtype, glossy2, glossy2-like, and glossy2; glossy2-like double mutant maize plants grown in summer 2024. Cuticular wax loads were the same across genotypes, whereas cuticular wax composition differed across genotypes and tissue types. In leaves, production of wax constituents above 30 carbons in length was reduced by greater than 50% in the glossy2 mutant and glossy2; glossy2-like double mutants. In silks, where hydrocarbons are the primary cuticular wax component, production of wax constituents above 28 carbons in length was reduced by over 1/3 in double mutants. To assess the cuticle’s function as a water barrier, water loss assays were performed on both leaves and silks. We observed significantly more water loss (2 mL of water per gram of dry silk tissue) from silks of the double mutant compared to the other three genotypes. This suggests that hydrocarbons are an important component of the water barrier properties conveyed by the silk cuticle. Ultimately, as we uncover the functions of genes involved in cuticle composition and function, we can design breeding and engineering strategies for the synthesis of “designer” cuticles suited to different environments.