Abstract
Compression wood (CW) in gymnosperm brings great difficulties to wood industry using wood as raw materials since CW presents special wood structure and have different physical and chemical properties from those of normal wood (NW). Chinese fir (Cunninghamia lanceolata) is widely distributed in China. However, global transcriptome profiling of coding and long non-coding RNA in response to compression stress has not been reported in the gymnosperm species. In this study, we revealed that CW in Chinese fir exhibited distinct morphology and cytology properties compared with those of NW, including high lignin content, thick and round tracheid cells. Furthermore, we combined both PacBio long-read SMRT sequencing (Iso-Seq) and Illumina short-read RNA-Seq to reveal the transcriptome in stem-differentiating xylem (SDX) under different time points (2, 26, and 74 h) upon compression stress in NW, CW, and OW (opposite wood), respectively. Iso-Seq was successfully assembled into 41,253 de-novo full-length transcriptome reference (average length 2,245 bp). Moreover, there were striking differences in expression upon compression stress, which were involved 13 and 7 key enzyme genes in the lignin and cellulose synthesis, respectively. Especially, we revealed 11 secondary growth-related transcription factors show differential expression under compression stress, which was further validated by qRT-PCR. Finally, the correlation between 6,533 differentially expressed coding genes and 372 differentially expressed long non-coding RNAs (lncRNAs) indicates that these lncRNAs may affect cell wall biogenesis and xyloglucan metabolism. In conclusion, our results provided comprehensive cytology properties and full-length transcriptome profiling of wood species upon compression stress. Especially we explored candidate genes, including both coding and long non-coding genes, and provided a theoretical basis for further research on the formation mechanism of CW in gymnosperm Chinese fir.
Highlights
Wood plays a very important role in human society
In order to observe cell structure of the normal wood (NW), OW, and Compression wood (CW) in xylem of Chinese fir, the paraffin sections from straight and leaning trunks were observed by upright microscope, and the fresh slices after dehydrate were observed by scanning electron microscopy (Figure 2)
The tracheids in the CW were obviously elliptical or round, with intercellular spaces, and the tracheid cell wall showed a certain degree of thickening (Figure 2G), which were consistent with the results of earlier studies in European yew, red cedar, and Norway spruce (Burgert et al, 2004)
Summary
Wood plays a very important role in human society. The high cellulose content of wood makes it an essential source of raw materials for papermaking and biofuels production (Ragauskas et al, 2006). Trees develop a special woody tissue due to gravity stimulation or mechanical stress such as strong wind, heavy snow, unstable soil, etc. The cross-section of the trunk shows a kind of eccentricity, and one side of the concentric circle is wider (Ruelle, 2014). This special wood structure is called reaction wood (RW) (Dadswell and Wardrop, 1949), which can correct the growth of slanted branches and stems (Sinnott, 1952; Wilson and Archer, 1977)
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