Identification of rose phenylacetaldehyde synthase by functional complementation in yeast

Rose flowers, like flowers and fruits of many other plants, produce and emit the aromatic volatiles 2-phenylacetaldehyde (PAA) and 2-phenylethylalchohol (PEA) which have a distinctive flowery/rose-like scent. Previous studies in rose have shown that, similar to petunia flowers, PAA is formed from l-phenylalanine via pyridoxal-5′-phosphate-dependent l-aromatic amino acid decarboxylase. Here we demonstrate the use of a Saccharomyces cerevisiae aro10Δ mutant to functionally characterize a Rosa hybrida cv. Fragrance Cloud sequence (RhPAAS) homologous to petunia phenylacetaldehyde synthase (PhPAAS). Volatile headspace analysis of the aro10Δ knockout strain showed that it produces up to eight times less PAA and PEA than the WT. Expression of RhPAAS in aro10Δ complemented the yeast's mutant phenotype and elevated PAA levels, similar to petunia PhPAAS. PEA production levels were also enhanced in both aro10Δ and WT strains transformed with RhPAAS, implying an application for metabolic engineering of PEA biosynthesis in yeast. Characterization of spatial and temporal RhPAAS transcript accumulation in rose revealed it to be specific to floral tissues, peaking in mature flowers, i.e., coinciding with floral scent production and essentially identical to other rose scent-related genes. RhPAAS transcript, as well as PAA and PEA production in flowers, displayed a daily rhythmic behavior, reaching peak levels during the late afternoon hours. Examination of oscillation of RhPAAS transcript levels under free-running conditions suggested involvement of the endogenous clock in the regulation of RhPAAS expression in rose flowers.