Analysis of biosynthesis and composition of cuticular wax in wild type bilberry (Vaccinium myrtillus L.) and its glossy mutant

Cuticular wax plays an important role in fruits in protection against environmental stresses and desiccation. In this study, biosynthesis and chemical composition of cuticular wax in wild type (WT) bilberry fruit was studied during development and compared with its natural glossy type (GT) mutant. The cuticular wax load in GT fruit was comparable to WT fruit. In both fruits, triterpenoids were the dominant wax compounds with decreasing proportion during the fruit development accompanied with increasing proportion of aliphatic compounds. Gene expression studies supported the pattern of compound accumulation during fruit development. Genes CER26-like, FAR2, CER3-like, LTP, MIXTA, and BAS exhibited prevalent expression in fruit skin indicating role in cuticular wax biosynthesis and secretion. In GT fruit, higher proportion of triterpenoids in cuticular wax was accompanied by lower proportion of fatty acids and ketones compared to WT fruit as well as lower density of crystalloid structures on berry surface. Our results suggest that a marked reduction in ketones in cuticular wax may play a significant role in the formation of glossy phenotype leading to the loss of rod-like structures in epicuticular wax layer of GT fruit.