Brassinosteroids (BRs) are known to be essential regulators for wood formation in herbaceous plants and poplar, but their roles in secondary growth and xylem development are still not well-defined, especially in pines. Here, we treated Pinus massoniana seedlings with different concentrations of exogenous BRs, and assayed the effects on plant growth, xylem development, endogenous phytohormone contents and gene expression within stems. Application of exogenous BR resulted in improving development of xylem more than phloem, and promoting xylem development in a dosage-dependent manner in a certain concentration rage. Endogenous hormone determination showed that BR may interact with other phytohormones in regulating xylem development. RNA-seq analysis revealed that some conventional phenylpropanoid biosynthesis- or lignin synthesis-related genes were downregulated, but the lignin content was elevated, suggesting that new lignin synthesis pathways or other cell wall components should be activated by BR treatment in P. massoniana. The results presented here reveal the foundational role of BRs in regulating plant secondary growth, and provide the basis for understanding molecular mechanisms of xylem development in P. massoniana.

Masson pine (Pinus massoniana L.) is one of the most important resin-producing tree species in southern China. However, the molecular regulatory mechanisms of resin yield are still unclear in masson pine. In this study, an integrated analysis of transcriptome, proteome, and biochemical characteristics from needles of masson pine with the high and common resin yield was investigated. The results showed that chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl C), carotenoids (Car), glucose (Glu), gibberellin A9 (GA9), gibberellin A15 (GA15), and gibberellin A53 (GA53) were significantly increased, whereas fructose (Fru), jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-ILE), gibberellin A1 (GA1), gibberellin A3 (GA3), gibberellin A19 (GA19), and gibberellin A24 (GA24) were significantly decreased in the high resin yield in comparison with those in the common one. The integrated analysis of transcriptome and proteome showed that chlorophyll synthase (chlG), hexokinase (HXK), sucrose synthase (SUS), phosphoglycerate kinase (PGK), dihydrolipoamide dehydrogenase (PDH), dihydrolipoamide succinyltransferase (DLST), 12-oxophytodienoic acid reductase (OPR), and jasmonate O-methyltransferases (JMT) were consistent at the transcriptomic, proteomic, and biochemical levels. The pathways of carbohydrate metabolism, terpenoid biosynthesis, photosynthesis, and hormone biosynthesis may play crucial roles in the regulation of resin yield, and some key genes involved in these pathways may be candidates that influence the resin yield. These results provide insights into the molecular regulatory mechanisms of resin yield and also provide candidate genes that can be applied for the molecular-assisted selection and breeding of high resin-yielding masson pine.

The SPX domain-encoding proteins are believed to play important roles in phosphorus (Pi) homeostasis and signal transduction in plants. However, the overall information and responses of SPXs to phosphorus deficiency in pines, remain undefined. In this study, we screened the transcriptome data of Pinus massoniana in response to phosphorus deprivation. Ten SPX domain-containing genes were identified. Based on the conserved domains, the P. massoniana SPX genes were divided into four different subfamilies: SPX, SPX-MFS, SPX-EXS, and SPX-RING. RNA-seq analysis revealed that PmSPX genes were differentially expressed in response to phosphorus deprivation. Furthermore, real-time quantitative PCR (RT-qPCR) showed that PmSPX1 and PmSPX4 showed different expression patterns in different tissues under phosphorus stress. The promoter sequence of 2284 bp upstream of PmSPX1 was obtained by the genome walking method. A cis-element analysis indicated that there were several phosphorus stress response-related elements (e.g., two P1BS elements, a PHO element, and a W-box) in the promoter of PmSPX1. In addition, the previously obtained PmSPX2 promoter sequence contained a W-box, and it was shown that PmWRKY75 could directly bind to the PmSPX2 promoter using yeast one-hybrid analysis in this study. These results presented here revealed the foundational functions of PmSPXs in maintaining plant phosphorus homeostasis.

Secondary growth is the main source of wood accumulation and has an extremely complex regulation process. Pinus massoniana Lamb. is one of the main timber tree species in China and it is of great significance in the study of the secondary growth process. The full-length transcriptome from the stems of P. massoniana with different diameter growth rates was obtained by PacBio and 15,448 full-length transcripts were identified. A comparative transcriptome analysis revealed that 408 genes were differentially expressed between the fast-growing wood (FGW) and slow-growing wood (SGW). The important regulatory genes involved in the secondary growth of P. massoniana (cell division, cell wall biosynthesis, lignification, and programmed cell death), such as ARL8, POD, EXPA8, Ecm33, and RhoA, were identified by a GO and KEGG annotation analysis. The differential expression of the key genes in the lignin synthesis pathway were obtained, such as PAL, 4CL, CCR, HCT, and PER. In addition, the abscisic acid receptor gene PYL and the ethylene biosynthesis key gene EFE were screened for their involvement in the regulation of the secondary growth of P. massoniana. It is speculated that these genes coordinate the processes of secondary growth to promote the rapid growth of FGW. This study preliminarily explored the differential mechanism of the growth rate of P. massoniana and provided a reference for obtaining new P. massoniana germplasm with a high quality and excellent yield.

Background: Lonicera macranthoides (L. macranthoides) is a traditional Chinese medicinal plant, the flower buds of which are rich in bioactive compounds, such as chlorogenic acids (CGAs) and flavonoids, and exhibit diverse pharmacological activities. Methods: Integrated transcriptomic and metabolomic analyses were conducted across three floral developmental stages: flower bud (FB), white flower (WF), and golden flower (GF). Results: Clustering analysis revealed distinct molecular profiles, with the WF and GF stages clustering together and clearly separating from the FB stage. The most significant metabolomic variation was observed between the GF and FB stages. KEGG enrichment analysis consistently highlighted the phenylpropanoid biosynthesis pathway as a key hub. Stage-specific accumulation patterns were identified for critical metabolites: caffeoylquinic acid peaked at the WF stage, while ferulic acid, sinapic acid, cinnamic acid, and p-coumaric acid reached their highest levels at the GF stage. Within this pathway, we identified 11 DEGs encoding the core enzymes, alongside 15 associated DAMs. The expression trends of four PAL genes were fully consistent with the accumulation of related precursors, and F5H expression correlated with its downstream product, sinapic acid. WGCNA identified a key module highly correlated with key phenolic acids, containing 71 transcription factors, including MYB, bHLH, WRKY, and AP2/ERF families, potentially forming a complex regulatory network for phenylpropanoid biosynthesis. Conclusions: This study deciphers the stage-specific regulatory network of CGA biosynthesis, providing critical insights and genetic resources for cultivating high-medicinal-content varieties of L. macranthoides.