Guang Yang

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.

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.