Combined morphological and transcriptomic analyses reveal genetic regulation underlying the species-specific bulbil outgrowth in Dioscorea alata L

In yam (Dioscorea spp) species, bulbil at leaf axils is the most striking species-specific axillary structure and exhibits important ecological niches as well as crop yields. Genetic regulation underlying bulbil outgrowth remain largely unclear. We here first characterized the development of bulbil from Dioscorea alata L. using histological analysis and further performed full transcriptional profiling on its key developmental stages. Comprehensive mRNA analyses suggested that long-distance phytohormone signals including auxin, CK and ABA, play critical roles in controlling the initiation of bulbil through coordinately altering expression levels of genes involved in localized hormone metabolism and transport. Sucrose functioned as a novel signal and was required strongly at the early stage of bulbil formation, thus promoting its outgrowth through up-regulating trehalose-6-phophate pathway. GO pathway analysis demonstrated that genes are enriched in biological processes related to light stimuli, cell division, cell wall modification and carbohydrate metabolism. Particularly, some novel genes including dioscorin A/B, starch synthetic enzymes and chitinases showed remarkably high expression levels and strengthened the outgrowth of bulbil. Our data set demonstrated that the initiation of bulbil was highly regulated by a large number of transcriptional regulators. RNA in situ hybridization with MYB, WRKY and NAC transcription factors confirmed their key roles in triggering bulbil initiation. Together, our findings provide a crucial angle for genetic regulation of controlling the unique reproductive development of bulbils. Transcriptome data set can serve as a valuable genomic resource for yam research community or further genetic manipulation to improve bulbil yields.\n\nHighlightTranscriptomic data identified multiple functional genes and regulators; long-distance signals (auxin, CK, ABA), and sucrose as a novel signal play critical roles in controlling bulbil outgrowth.