The properties of teak wood, such as natural durability and beautiful color, are closely associated with wood extractives. In order to further understand the performance differences between teak heartwood and sapwood, we analyzed the chemical components of extractives from 12 wood samples using an ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS)-based metabolomics approach. In total, 691 metabolites were identified, and these were classified into 17 different categories. Clustering analysis and principal component analysis of metabolites showed that heartwood samples could be clearly separated from sapwood samples. Differential metabolite analysis revealed that the levels of primary metabolites, including carbohydrates, amino acids, lipids, and nucleotides, were significantly lower in the heartwood than in the sapwood. Conversely, many secondary metabolites, including flavonoids, phenylpropanoids, and quinones, had higher levels in the heartwood than in the sapwood. In addition, we detected 16 specifically expressed secondary metabolites in the heartwood, the presence of which may correlate with the durability and color of teak heartwood. Our study improves the understanding of differential metabolites between sapwood and heartwood of teak, and provides a reference for the study of heartwood formation.

Soil bacterial communities play crucial roles in ecosystem functions and biogeochemical cycles of fundamental elements and are sensitive to environmental changes. However, the response of soil bacterial communities to chronosequence in tropical ecosystems is still poorly understood. This study characterized the structures and co-occurrence patterns of soil bacterial communities in rhizosphere and bulk soils along a chronosequence of teak plantations and adjacent native grassland as control. Stand ages significantly shifted the structure of soil bacterial communities but had no significant impact on bacterial community diversity. Bacterial community diversity in bulk soils was significantly higher than that in rhizosphere soils. The number of nodes and edges in the bacterial co-occurrence network first increased and then decreased with the chronosequence. The number of strongly positive correlations per network was much higher than negative correlations. Available potassium, total potassium, and available phosphorus were significant factors influencing the structure of the bacterial community in bulk soils. In contrast, urease, total potassium, pH, and total phosphorus were significant factors affecting the structure of the bacterial community in the rhizosphere soils. These results indicate that available nutrients in the soil are the main drivers regulating soil bacterial community variation along a teak plantation chronosequence.

Plant somatic embryogenesis (SE) is an efficient regeneration system for propagation. It involves the regulation of a complex molecular regulatory network encompassing endogenous hormone synthesis, metabolism, and signal transduction processes, induced through exogenous plant growth regulators. Previous studies have focused primarily on traditional propagation methods for Tectona grandis, but there is limited knowledge on SE and its hormonal regulatory mechanisms. In our study, different SE stages, including the nonembryogenic callus (NEC), embryogenic callus (EC), and globular and heart-shaped embryo (E-SEs) stages, were induced in teak cotyledons incubated on MS medium supplemented with 0.1 mg/L thidiazuron (TDZ). Morphological and histological observations indicated that EC primarily originates from the development of embryogenic cell clusters. During SE induction, the levels of six classes of endogenous hormones, IAA, CTK, ETH, ABA, SA, and JA, changed significantly. Transcriptome analysis revealed that endogenous hormones participate in SE induction in teak through various biological processes, such as biosynthesis, metabolism, and signal transduction pathways. We found that IAA biosynthesis primarily occurs through the IAM pathway during these three stages. The ETH receptor kinase gene SERF1 exhibited the highest expression levels in E-SEs. The ABA-, SA-, and JA-related signal transduction genes ABI3, NPR1, and JAZ exhibited no differential expression during different stages. Moreover, key encoding genes of SE regulators, including WUS, WOX and SERK, were differentially expressed during SE. In conclusion, this study offers insights into the roles of endogenous hormones and their interactions during SE induction.

Teak is a rare tropical tree with high economic value, and it is one of the world’s main afforestation trees. Low temperature is the main problem for introducing and planting this species in subtropical or temperate zones. Low-temperature acclimation can enhance the resistance of teak to low-temperature stress, but the mechanism for this is still unclear. We studied the gene expression of two-year-old teak seedlings under a rapid temperature drop from 20 °C to 4 °C using RNA-seq and WGCNA analyses. The leaves in the upper part of the plants developed chlorosis 3 h after the quick transition, and the grades of chlorosis were increased after 9 h, with the addition of water stains and necrotic spots. Meanwhile, the SOD and proline contents in teak leaves increased with the prolonged cold stress time. We also identified 36,901 differentially expressed genes, among which 1055 were novel. Notably, CBF2 and CBF4 were significantly induced by low temperatures, while CBF1 and CBF3 were not. Furthermore, WGCNA successfully identified a total of fourteen modules, which consist of three modules associated with cold stress response genes, two modules linked to CBF2 and CBF4, and one module correlated with the CBF-independent pathway gene HY5. The transformation experiments showed that TgCBF2 and TgCBF4 improved cold resistance in Arabidopsis plants.

Teak is a precious hardwood species in tropical and subtropical regions with a long growth cycle and slow economic returns. Intercropping medicinal plants is an effective method for obtaining early returns during the growth period of teak. However, currently, we lack sufficient knowledge about the impact of intercropping on the soil microenvironment, especially on rhizosphere soil bacterial communities. We selected two medicinal plants Alpinia katsumadai Hayata and Amomum longiligulare T.L. Wu, for an intercropping experiment with teak, and the non-intercropping teak forest area was used for comparison. By collecting soil rhizosphere samples and conducting 16S rDNA sequencing and property analysis, we aimed to investigate the influence of teak intercropping on soil microbial communities. The results showed that intercropping significantly improved soil nutrients contents, such as soil organic matter, soil total potassium and soil available nitrogen, and significantly altered bacterial community structure. Co-occurrence network analysis revealed that intercropping tightened the connections of the soil bacterial network and increased its complexity (by increasing the number of nodes and the proportion of positive edges). Teak intercropping with Amomum longiligulare T.L. Wu resulted in tighter network connections than teak intercropping with A. katsumadai Hayata. Changes in the soil bacterial community structure may related to environmental factors such as total potassium content and pH. These results demonstrated that the introduction of medicinal plants exerts a significant impact on the soil bacterial community of teak, fostering the enrichment of specific bacterial taxa (such as Firmicutes and Methylomirabilota), and makes the rhizosphere bacterial network denser and more complex. This study provides valuable insights for the management of teak plantations.

Calmodulin-binding transcription activator (CAMTA) proteins play significant roles in signal transduction, growth and development, as well as abiotic stress responses, in plants. Understanding their involvement in the low-temperature stress response of teak is vital for revealing cold resistance mechanisms. Through bioinformatics analysis, the CAMTA gene family in teak was examined, and six CAMTA genes were identified in teak. The encoded proteins were predicted to be located in the nucleus and exhibited hydrophilic properties, with molecular weights ranging from 103.4 to 123.3 kDa and isoelectric points ranging from 5.49 to 7.55. On the basis of protein sequence homology, the CAMTA family could be divided into three subgroups. Domain and 3D structure analyses demonstrated that all the TgCAMTA proteins contained the typical CAMTA domain with the CaMBD binding domain, which was exposed on the surface. Expression analysis of different tissues revealed the expression of TgCAMTA genes in teak roots, stems, leaves, flowers, fruits, and branches. Furthermore, the promoter region contained various cis-acting elements related to light, hormone, and abiotic stress responses. After low-temperature stress treatment, different expression patterns of TgCAMTAs were observed in teak roots, stems, and leaves, with TgCAMTA1 showing the highest expression level in leaves compared with stems. Transgenic lines carrying the TgCAMTA1/3 promoter::GUS construct cold stress induction of TgCAMTA1/3 genes revealed the presence of multiple low-temperature responsive cis-acting elements in the TgCAMTA1/3 promoter region. Subcellular localization analysis indicated that these genes were functional predominantly in the nucleus. Compared with wild-type Arabidopsis, TgCAMTA1/3-overexpressing Arabidopsis presented increased tolerance to freezing stress, with increased expression of AtCOR genes. Moreover, under low-temperature conditions, TgCAMTA3-overexpressing Arabidopsis presented significantly elevated expression levels of genes related to the CBF signaling pathway, including AtCBF1/2/3. Our findings add significantly to the existing knowledge regarding cold stress tolerance and help elucidate cold response mechanisms in teak.