What's that smell? The putrid scent of Rafflesia consueloae, its origin and developmental regulation

We report the floral scent composition of the endophytic holoparasite Rafflesia consueloae for the first time. Using a non-destructive in situ method that we developed, we identified 13 volatile compounds present in the scent of R. consuelaoe. Among the compounds detected were several benzenoids, organosilicons, an oligosulfide, a monoterpenoid, and a fatty acid-derived compound. Comparing the scent profiles of different reproductive stages, we found that all stages produced a similar set of volatiles, except for the flowers in bloom. The sulfur-containing dimethyl disulfide (DMDS), which is mainly responsible for the rotten smell of the flower, was only detected in the scent of full-bloom flowers indicating that its synthesis only takes place when the aperture is fully open and the flies are able to access the sex organs. Moreover, an analysis of the scent components of different floral parts from full-bloom flowers revealed that the different floral structures had varying scent profiles. The diaphragm and chamber floor produced the most volatiles. Notably, DMDS was only detected from the diaphragm and the central disk. Emission of putrid-smelling volatiles in these tissues may lure the flies into entering the floral chamber where the reproductive structures are located, thus increasing pollination success. Overall, this pioneering study of the R. consueloae floral scent composition provides valuable insights into the pollination mechanisms of the enigmatic Rafflesia genus and parasitic floral ecology in general.