Genetic interaction between <i>GL15</i> and <i>FDL1</i> modulates juvenile cuticle deposition and leaf permeability in maize

The plant cuticle is a hydrophobic layer produced by the epidermis of primary aerial tissues that serves as the primary barrier between the plant surface and the external environment, whose main function is to limit water loss. This study investigated the roles and interactions between the regulatory genes ZmFDL1 and ZmGL15 in modulating juvenile cuticle deposition and function in maize. Expression and lipid analyses, morphological studies, and permeability assays were performed on single and double mutants. Our results showed an additive effect of ZmFDL1 and ZmGL15 transcription factors on wax abundance and an epistatic effect of gl15-S on fdl1-1 in determining cutin deposition. ZmFDL1 has a key role in controlling juvenile cuticle deposition and preventing water loss, while the main role of ZmGL15 is to maintain a juvenile cuticle. Lack of ZmGL15 activity, as observed in the gl15-S mutant, results in the acquisition of a cuticle characterized by a higher cutin content, with increased ω-hydroxy fatty acids (FAs) as well as polyhydroxy FAs, and a lower wax content, with a decrease in both aldehydes and long-chain alcohols. These changes result in an increased water-holding capacity of the seedlings under drought stress conditions. Furthermore, gl15-S has an epistatic effect on the phenotype of the fdl1-1 mutant. In the double fdl1-1 gl15-S mutant, the absence of ZmGL15 activity mitigates the fdl1-1 morphological abnormalities and rescues the increased fdl1-1 cuticle-mediated leaf permeability.