Xu Tingting, Liu Zhao, Zhan Dingju, Pang Zhenwu, Zhang Shuwen, Li Chenhe, Kang Xiangyang, Yang Jun
State Key Laboratory of Tree Genetics and Breeding, National Engineering Research Center of Tree Breeding and Ecological Restoration, Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants of Ministry of Education, College of Biological Sciences and Technology, Beijing Forestry University, Beijing, 100083, China.
Guangxi Bagui R&D Institute for Forest Tree and Flower Breeding, Nanning, 530025, China.
Biotechnol Biofuels Bioprod. 2023 Jul 21;16(1):117. doi: 10.1186/s13068-023-02366-4.
Lignin is a major restriction factor for the industrial production of biomass resources, such as pulp and bioenergy. Eucalyptus is one of the most important sources of pulp and bioenergy. After polyploidization, the lignin content of forest trees is generally reduced, which is considered a beneficial genetic improvement. However, the differences in the lignin content between triploid and diploid Eucalyptus and the underlying regulatory mechanism are still unclear.
We conducted a comprehensive analysis at the phenotypic, transcriptional and metabolite levels between Eucalyptus urophylla triploids and diploids to reveal the effects of polyploidization on the lignin content and lignin metabolic pathway. The results showed that the lignin content of Eucalyptus urophylla triploid stems was significantly lower than that of diploids. Lignin-related metabolites were differentially accumulated between triploids and diploids, among which coniferaldehyde, p-coumaryl alcohol, sinapaldehyde and coniferyl alcohol had significant positive correlations with lignin content, indicating that they might be primarily contributing metabolites. Most lignin biosynthetic genes were significantly downregulated, among which 11 genes were significantly positively correlated with the lignin content and above metabolites. Furthermore, we constructed a co-expression network between lignin biosynthetic genes and transcription factors based on weighted gene co-expression network analysis. The network identified some putative orthologues of secondary cell wall (SCW)-related transcription factors, among which MYB52, MYB42, NAC076, and LBD15 were significantly downregulated in Eucalyptus urophylla triploids. In addition, potential important transcription factors, including HSL1, BEE3, HHO3, and NAC046, also had high degrees of connectivity and high edge weights with lignin biosynthetic genes, indicating that they might also be involved in the variation of lignin accumulation between triploid and diploid Eucalyptus urophylla.
The results demonstrated that some lignin-related metabolites, lignin biosynthetic genes and transcription factors in Eucalyptus urophylla triploids may be relatively sensitive in response to the polyploidization effect, significantly changing their expression levels, which ultimately correlated with the varied lignin content. The analysis of the underlying formation mechanism could provide beneficial information for the development and utilization of polyploid biomass resources, which will be also valuable for genetic improvement in other bioenergy plants.
木质素是纸浆和生物能源等生物质资源工业化生产的主要限制因素。桉树是纸浆和生物能源的最重要来源之一。多倍体化后，林木的木质素含量通常会降低，这被认为是一种有益的遗传改良。然而，三倍体和二倍体桉树之间木质素含量的差异及其潜在调控机制仍不清楚。
我们对尾叶桉三倍体和二倍体在表型、转录和代谢物水平上进行了全面分析，以揭示多倍体化对木质素含量和木质素代谢途径的影响。结果表明，尾叶桉三倍体茎中的木质素含量显著低于二倍体。三倍体和二倍体之间木质素相关代谢物存在差异积累，其中松柏醛、对香豆醇、芥子醛和松柏醇与木质素含量呈显著正相关，表明它们可能是主要的贡献代谢物。大多数木质素生物合成基因显著下调，其中11个基因与木质素含量及上述代谢物呈显著正相关。此外，我们基于加权基因共表达网络分析构建了木质素生物合成基因与转录因子之间的共表达网络。该网络鉴定出一些次生细胞壁（SCW）相关转录因子的假定直系同源物，其中MYB52、MYB42、NAC076和LBD15在尾叶桉三倍体中显著下调。此外，包括HSL1、BEE3、HHO3和NAC046在内的潜在重要转录因子与木质素生物合成基因也具有高度的连通性和高边权重，表明它们可能也参与了三倍体和二倍体尾叶桉之间木质素积累的变化。
结果表明，尾叶桉三倍体中一些与木质素相关的代谢物、木质素生物合成基因和转录因子可能对多倍体化效应相对敏感，其表达水平发生显著变化，并最终与木质素含量的变化相关。对潜在形成机制的分析可为多倍体生物质资源的开发利用提供有益信息，这对其他生物能源植物的遗传改良也具有重要价值。
