Chemical diversity of cuticular waxes in the honeysuckle family (Caprifoliaceae)

The above-ground organs of most land plants are covered by a hydrophobic cuticle, which limits non-stomatal water loss and protects against insect herbivores and pathogens. The cuticle consists of a cutin matrix associated with hydrocarbon-derived waxes. These waxes may accumulate on the outer surface of the cutin to form crystals with additional functional benefits. Many plant surfaces exhibit tubular crystals, formed by the secondary (sec.) alcohol nonacosan-10-ol. However, nonacosan-10-ol biosynthesis remains unknown in many plant species. This thesis aimed to expand the chemical inventory of cuticular waxes in the previously understudied honeysuckle family (Caprifoliaceae) and to investigate the biosynthesis of mid-chain-functionalized wax compounds, namely nonacosan-10-ol. Reports of epicuticular wax crystals and sparse literature suggest nonacosan-10-ol occurrence in the Caprifoliaceae, making it an ideal group for investigation. I first analyzed wax composition and leaf micromorphology in eight species across five Caprifoliaceae subfamilies (Chapter 3). I identified multiple mid-chain-functionalized compounds, occurring primarily in Valerianoideae and Caprifolioideae and used chemical data to propose diverse biosynthetic pathways of these compounds, including nonacosan-14-one and nonacosan-10-ol. I further identified relationships between these compounds and distinct crystal morphologies. I additionally characterized a unique group of compounds in Lonicera etrusca as short-chain-alkyl esters (Chapter 4). I then studied four Lonicera species to further investigate the nonacosan-10-ol occurrence and crystal structures within the genus (Chapter 5). Three Lonicera species contained sec. alcohol and sec./sec. alkanediol homologs and isomers in their waxes, associated with tubule crystals. From this data, I hypothesized nonacosan-10-ol is formed by P450-mediated hydroxylation of alkanes, and that co-crystallization of nonacosan-10-ol with alkanediols enhances tubule formation. Finally, I analyzed the distribution of mid-chain-functionalized compounds across four organ waxes of Lonicera ciliosa (Chapter 6). I found nonacosan-10-ol was produced in each organ, and sec./sec. alkanediols had distinct isomer patterns across organs, leading me to propose that alkanediols are formed via hydroxylation of sec. alcohols by multiple regiospecific hydroxylases. Overall, this work advances our knowledge of cuticular wax compositions in the Caprifoliaceae, particularly the Lonicera genus, and lays the foundation for further research into the biosynthesis of mid-chain-functionalized wax compounds that influence crystal formation, thus protecting plant surfaces.