The TALE gene family is a subfamily of the homeobox gene family and has been implicated in regulating plant secondary growth. However, reports about the evolutionary history and function of the TALE gene family in bamboo are limited. Here, the homeobox gene families of moso bamboo Olyra latifolia and Bonia amplexicaulis were identified and compared. Many duplication events and obvious expansions were found in the TALE family of woody bamboo. PhTALEs were found to have high syntenies with TALE genes in rice. Through gene co-expression analysis and quantitative real-time PCR analysis, the candidate PhTALEs were thought to be involved in regulating secondary cell wall development of moso bamboo during the fast-growing stage. Among these candidate PhTALEs, orthologs of OsKNAT7, OSH15, and SH5 in moso bamboo may regulate xylan synthesis by regulating the expression of IRX-like genes. These results suggested that PhTALEs may participate in the secondary cell wall deposition in internodes during the fast-growing stage of moso bamboo. The expansion of the TALE gene family may be implicated in the increased lignification of woody bamboo when divergent from herbaceous bamboos.

The neglect of Moso bamboo’s phenotype variations hinders its broader utilization, despite its high economic value globally. Thus, this study investigated the morphological variations of 16 Moso bamboo populations. The analysis revealed the culm heights ranging from 9.67 m to 17.5 m, with average heights under the first branch ranging from 4.91 m to 7.67 m. The total internode numbers under the first branch varied from 17 to 36, with internode lengths spanning 2.9 cm to 46.4 cm, diameters ranging from 5.10 cm to 17.2 cm, and wall thicknesses from 3.20 mm to 33.3 mm, indicating distinct attributes among the populations. Furthermore, strong positive correlations were observed between the internode diameter, thickness, length, and volume. The coefficient of variation of height under the first branch showed strong positive correlations with several parameters, indicating variability in their contribution to the total culm height. A regression analysis revealed patterns of covariation among the culm parameters, highlighting their influence on the culm height and structural characteristics. Both the diameter and thickness significantly contribute to the internode volume and culm height, and the culm parameters tend to either increase or decrease together, influencing the culm height. Moreover, this study also identified a significant negative correlation between monthly precipitation and the internode diameter and thickness, especially during December and January, impacting the primary thickening growth and, consequently, the internode size.

The Moso bamboo culm neck, connected with the rhizome and the shoot bud, is an important hub for connecting and transporting the aboveground and belowground systems of bamboo for the shoot bud development and rapid growth. Our previous study revealed that the culm neck generally undergoes six different developmental stages (CNS1–CNS6), according to the primary thickening growth of the underground shoot bud. However, the molecular mechanism of the culm neck development remains unknown. The present study focused on the developmental process of the CNS3–CNS5 stages, representing the early, middle, and late elongation stages, respectively. These stages are densely packed with vascular tissues and consist of epidermis, hypodermis, cortex, and ground tissue. Unlike the hollow structure of the culms, the culm necks are solid structures. As the culm neck continues to grow, the lignin deposition increases noticeably, contributing to its progressive strengthening. For the transcriptome analysis, a total of 161,160 transcripts with an average length of 2373 were obtained from these stages using both PacBio and Illumina sequencing. A total of 92.2% of the reads mapped to the Moso bamboo reference genome. Further analysis identified a total of 5524 novel genes and revealed a dynamic transcriptome. Secondary-metabolism- and transport-related genes were upregulated particularly with the growth of the culm neck. Further analysis revealed the molecular processes of lignin accumulation in the culm neck, which include differentially expressed genes (DEGs) related to cell wall loosening and remodeling and secondary metabolism. Moreover, the upregulations of transcription factors such as MYBH and RSM in the MYB family play crucial roles during critical transitions in the culm neck development, such as changes in the angle between the rhizome and the culm neck. Our new findings provide essential insights into the cellular roadmaps, transcriptional networks, and key genes involved in the culm neck development.

The lack of mutants due to the long periods between flowering of bamboo plants is one of the limiting factors inhibiting research progress in the culm development of bamboo plants. In this study, a stable new dwarf variant of Phyllostachys edulis (Moso bamboo), Phyllostachys edulis f. exaurita T. G. Chen, was discovered and was characterized morphologically, anatomically, and physiologically. The height, diameter at breast height, number of internodes, length and wall thickness of internodes, length, width and number of parenchyma cells of internodes, and morphology of the wide-type (WT) and dwarf variant vascular bundles were compared. The height of the variant was only 49% that of the WT Moso bamboo. It was concluded that the decrease in internode number and length was the cause of dwarfism in P. edulis f. exaurita. The decreased internode length was the result of a decrease in cell number and cell length in the internode. In addition, the laws of change of internode length, internode thickness, cell length, and cell number differed between the WT Moso bamboo and the variant. Furthermore, lower IAA and zeatin concentrations were detected in the buds of the variant. These results suggest that P. edulis f. exaurita is a variant with inhibited primary thickening growth, which is valuable for interpretating the molecular mechanisms underlying the primary thickening growth of bamboo that are still largely unknown.

The ATP-binding cassette subfamily B (ABCB) is an important transporter family, and many members are well known for their auxin transport function. However, reports on the function of the ABCB genes during Moso bamboo development are few. In this study, we identified and characterized 37 PhABCB genes in Moso bamboo and classified them into five subgroups, Ⅰ–Ⅴ. We further observed gene family expansion and gene loss events during the evolution of the PhABCB gene family. It was found that the expansion of the PhABCB family was mainly attributed to the whole-genome duplication and DNA-transposed duplication models. Gene co-expression analysis and quantitative real-time PCR revealed that several PhABCB genes may be involved in the development of the secondary cell wall (SCW) during the rapid growth of Moso bamboo. Through examining their expression in different parts of the bamboo internode where the cell walls exhibited different developmental stages, the roles of eight candidate PhABCBs in the SCW development were further characterized. Of the eight PhABCB genes, PhABCB7, PhABCB11, PhABCB14, and PhABCB21 may be involved in the SCW biogenesis in Moso bamboo. This study provides the basis for discovering the potential role of PhABCB genes in Moso bamboo cell wall development; further studies are needed to elucidate how these PhABCBs function in SCW development by regulating the polar transport of auxin.

Culm sheaths are capable of photosynthesis and are an important class of non-leaf organs in bamboo plants. The source–sink interaction mechanism has been found to play an important role in the interaction between culm sheaths and internodes in Bambusa multiplex. Research on the regulatory mechanisms of culm sheath senescence is important for the study of internode growth, but reports in this regard are limited. In this study, a weighted gene co-expression network analysis was performed on transcriptome data of B. multiplex culm sheaths at different developmental stages and identified some gene modules significantly related to the typical senescence stages (SS3 and SS4). Among these modules, one module significantly associated with both SS3 and SS4 was identified, and its hub gene (BmCCD8) was a key gene of the strigolactones (SLs) synthesis pathway. To verify the relationship between SLs and culm sheath senescence, we performed experiments such as detection of endogenous hormone, treatment with exogenous hormones, transmission electron microscopic observation and detection of gene expression levels. A positive relationship was found between the SL content and the degree of sheath senescence. Treatment with the artificial SL analog GR24 resulted in a significant decrease in chlorophyll content in the sheath, while treatment with the SL synthesis inhibitor Tis108 led to a significant increase in chlorophyll content. A different response pattern to exogenous GR24 and Tis108 was also observed in genes related to the chlorophyll degradation pathway. Chloroplasts were also found to begin degradation one day after the end of exogenous GR24 treatment. Thus, we concluded that SLs may regulate culm sheath senescence by promoting chlorophyll degradation.