Magnolia × soulangeana 'Changchun' are trees that bloom in spring and summer respectively after flower bud differentiation. Here, we use phenological and morphological observation and RNA-seq technology to study the molecular basis of flowering initiation in 'Changchun'. During the process of flowering initiation in spring and summer, the growth of expanded flower buds increased significantly, and their shape was obviously enlarged, which indicated that flowering was initiated. A total of 168,120 expressed genes were identified in spring and summer dormant and expanded flower buds, of which 11,687 genes showed significantly differential expression between spring and summer dormant and expanded flower buds. These differentially expressed genes (DEGs) were mainly involved in plant hormone signal transduction, metabolic processes, cellular components, binding, and catalytic activity. Analysis of differential gene expression patterns revealed that gibberellin signaling, and some transcription factors were closely involved in the regulation of spring and summer flowering initiation in 'Changchun'. A qRT-PCR (quantitative Real Time Polymerase Chain Reaction) analysis showed that BGISEQ-500 sequencing platform could truly reflect gene expression patterns. It also verified that GID1B (GIBBERELLIN INSENSITIVE DWARF1 B), GID1C, SPL8 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 8), and GASA (GIBBERELLIC ACID-STIMULATED ARABIDOPSIS) family genes were expressed at high levels, while the expression of SPY (SPINDLY) was low during spring and summer flowering initiation. Meanwhile, the up-and down-regulated expression of, respectively, AGL6 (AGAMOUS-LIKE 6) and DREB3 (DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 3), AG15, and CDF1 (CYCLIC DOF FACTOR 1) might also be involved in the specific regulation of spring and summer flowering initiation. Obviously, flowering initiation is an important stage of the flowering process in woody plants, involving the specific regulation of relevant genes and transcription factors. This study provides a new perspective for the regulation of the flowering process in perennial woody plants.Genes 2020, 11, 15 2 of 18 Using Solexa/Illumina sequencing platform, researchers have identified almost all transcripts involved in flowering from the vegetative and flower buds in Dimocarpus longan, including putative homologues of DELLA protein, LFY (LEAFY), SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO1) [2]. Meanwhile, compared to the apical meristem of vegetative growth, gibberellin 3 beta-hydroxylase 2 and LFY were both expressed higher in early flowering, indicated that GA pathway may be related to the early flowering of Angelica sinensis [3]. By comparing the differences in transcript expression levels between flowering and non-flowering Moso bamboo samples at different flowering developmental stages, researchers found that GAMYB, GID1 (GIBBERELLIN INSENSITIVE DWARF1), and GID2 were significantly up-regulated, while DELLA protein was down-regulated, and believed that bamboo flowering was associated with gibbere...
