De novo transcriptome sequencing in Ficus hirta Vahl. (Moraceae) to investigate gene regulation involved in the biosynthesis of pollinator attracting volatiles

Flower volatile organic compounds (VOCs) emitted from the receptive figs of Ficus (Moraceae) play important roles in maintaining the specificity of pollinator attraction and reproductive isolation between host species. The dominant components of VOCs are terpenoids, and while the genes involved in terpenoid biosynthesis are known, we know very little about the regulation of these genes and its relationship to pollinator attraction in Ficus . Thus, we selected pre-receptive (pre-VOC attractant-emitting) and receptive (VOC attractant-emitting) phase female flowers of a dioecious fig for transcriptome sequencing to investigate the differential activity of genes, including those related to terpenoid biosynthesis. We annoted 53,445 unigenes, of which 608 were found to be differently expressed in the two stages, with 242 unigenes upregulated and 366 unigenes downregulated in pre-receptive relative to receptive phase flowers. With respect to the production of VOCs, 80 unigenes encoded 34 enzyme-coding genes involved in terpenoid biosynthesis, including nearly all key enzymes of the MVA and MEP pathways forming the backbone of terpenoid biosynthesis. We designed pair primers for 16 of these 34 enzyme genes and validated 5 of them in 30 Ficus species representing 6 subgenera. In addition to the transcript sequences, we identified 35,558 putative microsatellite loci and designed primers for 11,468 of them. Our data and results will contribute to genetic research on terpene biosynthesis in figs and will aid in the understanding of the morphological and chemical changes that occur as the female flowers develop and produce pollinator-specific VOCs.