Comprehensive Biochemical, Physiological, and Transcriptomic Analyses Provide Insights Into Floral Bud Dormancy in Rhododendron delavayi Franch

Due to a scarcity of relevant data, the ornamental woody flower Rhododendron delavayi Franch. is examined in the current study for its low temperature-induced floral bud dormancy (late October–end December) aspect. This study used transcriptome data profiling and co-expression network analyses to identify the interplay between endogenous hormones and bud dormancy phases such as pre-dormancy, para-dormancy, endo-dormancy, eco-dormancy, and dormancy release. The biochemical and physiological assays revealed the significance of the abundance of phytohormones (abscisic acid, auxin, zeatin, and gibberellins), carbohydrate metabolism, oxidative species, and proteins (soluble proteins, proline, and malondialdehyde) in the regulatory mechanism of floral bud dormancy. The transcriptome sequencing generated 65,531 transcripts, out of which 504, 514, 307, and 240 expressed transcripts were mapped uniquely to pre-, para-, endo-, and eco-phases of dormancy, showing their roles in the stimulation of dormancy. The transcripts related to LEA29, PGM, SAUR family, RPL9e, ATRX, FLOWERING LOCUS T, SERK1, ABFs, ASR2, and GID1 were identified as potential structural genes involved in floral bud dormancy. The transcription factors, including Zinc fingers, CAD, MADS-box family, MYB, and MYC2, revealed their potential regulatory roles concerning floral bud dormancy. The gene co-expression analysis highlighted essential hub genes involved in cold stress adaptations encoding proteins, viz, SERPIN, HMA, PMEI, LEA_2, TRX, PSBT, and AMAT. We exposed the connection among low temperature-induced dormancy in floral buds, differentially expressed genes, and hub genes via strict screening steps to escalate the confidence in selected genes as being truly putative in the pathways regulating bud dormancy mechanism. The identified candidate genes may prove worthy of further in-depth studies on molecular mechanisms involved in floral bud dormancy of Rhododendron species.