Bamboo plants have a distinctive life cycle with long flowering periodicity. Many species remain in vegetative growth for decades, followed by large-scale flowering and subsequent death. Floral transition is activated while shoot buds are still dormant in bamboo plants. In this study, we performed morphological characterization and transcriptome analysis of the shoot buds at different growth stages from flowering and non-flowering Pleioblastus pygmaeus. The morphological and anatomical structures of the dormant shoot buds were similar in flowering and non-flowering plants, while there was an obvious difference between the flower buds from flowering plants and the leaf buds from non-flowering plants. The transcriptomes of the dormant shoot buds, germinated shoots, and flower buds from flowering P. pygmaeus, and the dormant shoot buds, germinated shoots, and leaf buds from non-flowering P. pygmaeus were profiled and compared by RNA-Seq. The identified sequences were mostly related to metabolic synthesis, signal transmission, translation, and other functions. A total of 2434 unigenes involved in different flowering pathways were screened from transcriptome comparisons. The differentially expressed unigenes associated with the photoperiod pathway were related to circadian rhythm and plant hormone signal transduction. Moreover, the relative expression levels of a few key flowering-related genes such as CO, FT, FLC, and SOC1 were quantified by qRT-PCR, which was in accordance with RNA-Seq. The study revealed morphological differences in the shoot buds at different growth stages and screened flowering-related genes by transcriptome comparisons of the shoot buds from flowering and non-flowering P. pygmaeus, which will enrich the research on reproductive biology of bamboo plants and shed light on the molecular mechanism of the floral transition in bamboo plants.

The plant-specific transcription factors TEOSINTE BRANCHED1/CYCLO IDEA/PROLIFERATING CELL FACTOR1 (TCP) act as developmental regulators that have many roles in the growth and development processes throughout the entire life span of plants. TCP transcription factors are responsive to endogenous and environmental signals, such as salt stress. However, studies on the role of the TCP genes in salt stress response have rarely focused on woody plants, especially forest trees. In this study, the BpTCP3 gene, a CYC/TB1 subfamily member, isolated from Betula platyphylla Sukaczev, was significantly influenced by salt stress. The β-glucuronidase (GUS) staining analysis of transgenic B. platyphylla harboring the BpTCP3 promoter fused to the reporter gene GUS (pBpTCP3::GUS) further confirmed that the BpTCP3 gene acts a positive regulatory position in salt stress. Under salt stress, we found that the BpTCP3 overexpressed lines had increased relative/absolute high growth but decreased salt damage index, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) levels versus wild-type (WT) plants. Conversely, the BpTCP3 suppressed lines exhibited sensitivity to salt stress. These results indicate that the BpTCP3 transcription factor improves the salt tolerance of B. platyphylla by reducing reactive oxygen species damage, which provides useful clues for the functions of the CYC/TB1 subfamily gene in the salt stress response of B. platyphylla.