Leaf surface wax composition of genetically diverse mulberry (Morus sp.) genotypes and its close association with expression of genes involved in wax metabolism

Silkworm (Bombyx mori), the primary producer of silk, has strong feeding preference for most turgid and hydrated mulberry leaves. In a previous study, we showed positive correlation between moisture retention capacity (MRC) of the mulberry leaf and leaf surface wax amount. In the present study, we examined wax constituents in genotypes that exhibited a wide range of leaf surface wax amount and MRC. Gas chromatographic analysis revealed that acids, alkanes, aldehydes, primary alcohols, iso-alkanes, triterpenoids and esters were among mulberry waxes identified and the major being alkanes. The highest total leaf wax amount was 1006.8 mu g dm(-2) in the V1 genotype whereas S-36 had the least wax at 436.9 mu g dm(-2). The alkanes were dominated by those having 25, 27, 29, 31 and 33 carbons, with C-31 compounds being the most abundant. RNA-blot hybridization performed with 13 wax biosynthesis associated genes using heterologous probes revealed a close association between surface wax composition and expression levels of genes associated with wax elongation (CUT1, KCS1). The association was also established with homologous probes of KCS1, WAX2, CUT1 and LTP1-like genes. In summary, regulation of early wax precursor metabolism is a likely contributor to the variation observed in leaf wax composition in mulberry.