State Key Laboratory of Tree Genetics and Breeding (Northeast Forestry University), Harbin, China.
PLoS One. 2014 Feb 20;9(2):e87566. doi: 10.1371/journal.pone.0087566. eCollection 2014.
Betula platyphylla Suk (birch) is a fast-growing woody species that is important in pulp industries and the biofuels. However, as an important pulp species, few studies had been performed on its wood formation. In the present study, we investigated the molecular responses of birch xylem to artificial bending and gravitational stimuli. After trunks of birch trees were subjected to bending for 8 weeks, the cellulose content was significantly greater in tension wood (TW) than in opposite wood (OW) or normal wood (NW), whereas the lignin content in TW was significantly lower than that in OW and NW. In addition, TW grew more rapidly than OW and generated TW-specific fibers with an additional G-layer. Three transcriptome libraries were constructed from TW, OW and NW of B. platyphylla, respectively, after the plants were subjected to artificial bending. Overall, 80,909 nonredundant unigenes with a mean size of 768 nt were assembled. Expression profiles were generated, and 9,684 genes were found to be significantly differentially expressed among the TW, OW and NW libraries. These included genes involved in secondary cell wall structure, wood composition, and cellulose or lignin biosynthesis. Our study showed that during TW formation, genes involved in cellulose synthesis were induced, while the expression of lignin synthesis-related genes decreased, resulting in increased cellulose content and decreased lignin levels in TW. In addition, fasciclin-like arabinogalactan proteins play important role in TW formation. These findings may provide important insights into wood formation at the molecular level.
白桦（Betula platyphylla Suk）是一种生长迅速的木本植物，在纸浆工业和生物燃料中具有重要地位。然而，作为一种重要的纸浆树种，其木材形成的研究较少。本研究调查了白桦木质部对人工弯曲和重力刺激的分子响应。白桦树干经过 8 周的弯曲后，拉伸木（TW）的纤维素含量明显高于对向木（OW）和正常木（NW），而 TW 的木质素含量明显低于 OW 和 NW。此外，TW 的生长速度快于 OW，并产生具有额外 G 层的 TW 特异性纤维。在人工弯曲后，分别从 TW、OW 和 NW 构建了三个白桦转录组文库。总体而言，组装了 80909 个非冗余的平均大小为 768nt 的非冗余基因。生成了表达谱，发现 9684 个基因在 TW、OW 和 NW 文库之间差异表达显著。这些基因包括参与次生细胞壁结构、木材成分以及纤维素或木质素生物合成的基因。本研究表明，在 TW 形成过程中，参与纤维素合成的基因被诱导，而与木质素合成相关的基因表达减少，导致 TW 中纤维素含量增加，木质素水平降低。此外，纤维蛋白样阿拉伯半乳聚糖蛋白在 TW 形成中起重要作用。这些发现可能为木质部形成提供重要的分子水平的见解。
