Roles of the and Genes in Cuticle Biosynthesis and Potential Impacts on Growth on Maize Silks

Maize silks, the stigmatic portions of the female flowers, have an important role in reproductive development. Silks also provide entry points for pathogens into host tissues since fungal hyphae move along the surface of the silks to reach the site of infection, i.e., the developing kernel. The outer extracellular surface of the silk is covered by a protective hydrophobic cuticle, comprised of a complex array of long-chain hydrocarbons and small amounts of very long chain fatty acids and fatty alcohols. This work illustrates that two previously characterized cuticle-related genes separately exert roles on maize silk cuticle deposition and function. / () MYB transcription factor is a key regulator of cuticle deposition in maize seedlings. The () gene, a putative member of the BAHD superfamily of acyltransferases with close sequence similarity to the Arabidopsis gene, is involved in the elongation of the fatty acid chains that serve as precursors of the waxes on young leaves. In silks, lack of action generates a decrease in the accumulation of a wide number of compounds, including alkanes and alkenes of 20 carbons or greater and affects the expression of cuticle-related genes. These results suggest that retains a regulatory role in silks, which might be exerted across the entire wax biosynthesis pathway. Separately, a comparison between and wild-type silks reveals differences in the abundance of specific cuticular wax constituents, particularly those of longer unsaturated carbon chain lengths. The inferred role of is to control the chain lengths of unsaturated hydrocarbons. The treatment of maize silks with conidia suspension results in altered transcript levels of and genes. In addition, an increase in fungal growth was observed on mutant silks 72 hours after infection. These findings suggest that the silk cuticle plays an active role in the response to infection.