Catalpa bungei is an economically important tree with high-quality wood and highly valuable to the study of wood formation. In this work, the xylem microstructure of C. bungei tension wood (TW) was observed, and we performed transcriptomics, proteomics and Raman spectroscopy of TW, opposite wood (OW) and normal wood (NW). The results showed that there was no obvious gelatinous layer (G-layer) in the TW of C. bungei and that the secondary wall deposition in the TW was reduced compared with that in the OW and NW. We found that most of the differentially expressed mRNAs and proteins were involved in carbohydrate polysaccharide synthesis. Raman spectroscopy results indicated that the cellulose and pectin content and pectin methylation in the TW were lower than those in the OW and NW, and many genes and proteins involved in the metabolic pathways of cellulose and pectin, such as galacturonosyltransferase (GAUT), polygalacturonase (PG), endoglucanase (CLE) and β-glucosidase (BGLU) genes, were significantly upregulated in TW. In addition, we found that the MYB2 transcription factor may regulate the pectin degradation genes PG1 and PG3, and ARF, ERF, SBP and MYB1 may be the key transcription factors regulating the synthesis and decomposition of cellulose. In contrast to previous studies on TW with a G-layer, our results revealed a change in metabolism in TW without a G-layer, and we inferred that the change in the pectin type, esterification and cellulose characteristics in the TW of C. bungei may contribute to high tensile stress. These results will enrich the understanding of the mechanism of TW formation.

Conifers are the largest and most ubiquitous group of gymnosperms and have significant ecological significance and economic importance. However, the huge and complex genomes have hindered the sequencing and mining of conifer genomes. In this study, we identified 413 423 transposable elements (TEs) from Picea abies, Picea glauca and Pinus taeda using a combination of multiple approaches and classified them into 11 133 families. A comprehensive web-based database, ConTEdb, was constructed and served for researchers. ConTEdb enables users to browse, retrieve and download the TE sequences from the database. Several analysis tools are integrated into ConTEdb to help users mine the TE data easily and effectively. In summary, ConTEdb provides a platform to study TE biology and functional genomics in conifers.

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