Gene Regulatory Networks for Lignin Biosynthesis in Switchgrass (Panicum virgatum)

First author: Xiaolan Rao; Affiliations: University of North Texas (北德克萨斯州大学): Denton, Texas

Corresponding author: Richard A. Dixon

Cell wall recalcitrance is the major challenge to improving saccharification efficiency (糖化效率) in converting lignocellulose (木质纤维素) into biofuels (生物燃料). However, information regarding the transcriptional regulation of secondary cell wall biogenesis remains poor in switchgrass (Panicum virgatum), which has been selected as a biofuel crop in the United States. In this study, we present a combination of computational and experimental approaches to develop gene regulatory networks for lignin formation in switchgrass. To screen transcription factors (TFs) involved in lignin biosynthesis, we developed a modified method to perform co‐expression network analysis using 14 lignin biosynthesis genes as bait (target) genes. The switchgrass lignin co‐expression network was further extended by adding 14 TFs identified in this study, and seven TFs identified in previous studies, as bait genes. Six TFs (PvMYB58/63, PvMYB42/85, PvMYB4, PvWRKY12, PvSND2 and PvSWN2) were targeted to generate overexpressing and/or downregulated transgenic switchgrass lines. The alteration of lignin content, cell wall composition and/or plant growth in the transgenic plants supported the role of the TFs in controlling secondary wall formation. RNA‐seq analysis of four of the transgenic switchgrass lines revealed downstream target genes of the secondary wall‐ elated TFs and crosstalk with other biological pathways. In vitro transactivation assays further confirmed the regulation of specific lignin pathway genes by four of the TFs. Our meta‐analysis provides a hierarchical network of TFs and their potential target genes for future manipulation of secondary cell wall formation for lignin modification in switchgrass.

细胞壁是提高木质纤维素转化为生物燃料时糖化效率的主要限制因素。然而，生物燃料作物柳枝稷中有关次生细胞壁的转录调控机制了解得还很少。本文结合了计算和试验方法对柳枝稷木质素形成的基因调控网络进行了研究。为了鉴定参与木质素生物合成的转录因子，作者利用14个木质素生物合成基因作为bait进行了共表达网络分析。通过加入另外14个本文鉴定的转录因子和先前鉴定的7个转录因子，作者进一步构建了木质素共表达网络。作者构建了PvMYB58/63、PvMYB42/85、PvMYB4、PvWRKY12、PvSND2和PvSWN2六个转录因子的过表达或下调表达的转基因柳枝稷株系。转基因株系中木质素含量、细胞壁组成及植株长势的改变进一步说明了这些TF在控制次生细胞壁形成中的作用。对于四个柳枝稷转基因株系的转录组测序分析显示次生细胞壁相关转录因子的下游靶基因以及与其它生物通路的交联。体外的转录激活试验进一步确认了这四个转录因子对特异的木质素通路基因的调控。作者的元分析提供了一个转录因子的分层调控网络，并为将来对柳枝稷次生细胞壁形成的改造提供了靶基因。

通讯：Richard A. Dixon (https://biology.unt.edu/people/richard-dixon-biochemistry-molecular-biology)

个人简介：牛津大学，生物化学学士；牛津大学，植物学硕士；牛津大学，博士。

研究方向：生物能源作物中木质素和细胞壁多聚物的改良；苜蓿饲料品质的改良；黄酮类化合物与人类健康。

doi: https://doi.org/10.1111/pbi.13000

Journal: Plant Biotechnology Journal

First Published: 22 August, 2018

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