Differentiation of Tracheary Elements in Sugarcane Suspension Cells Involves Changes in Secondary Wall Deposition and Extensive Transcriptional Reprogramming

19 páginas.- 7 figuras,. referencias.- The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpls.2020.617020/full#supplementary-material
Plant lignocellulosic biomass, mostly composed of polysaccharide-rich secondary cell walls (SCWs), provides fermentable sugars that may be used to produce biofuels and biomaterials. However, the complex chemical composition and physical structure of SCWs hinder efficient processing of plant biomass. Understanding the molecular mechanisms underlying SCW deposition is, thus, essential to optimize bioenergy feedstocks. Here, we establish a xylogenic culture as a model system to study SCW deposition in sugarcane; the first of its kind in a C4 grass species. We used auxin and brassinolide to differentiate sugarcane suspension cells into tracheary elements, which showed metaxylem-like reticulate or pitted SCW patterning. The differentiation led to increased lignin levels, mainly caused by S-lignin units, and a rise in p-coumarate, leading to increased p-coumarate:ferulate ratios. RNAseq analysis revealed massive transcriptional reprogramming during differentiation, with upregulation of genes associated with cell wall biogenesis and phenylpropanoid metabolism and downregulation of genes related to cell division and primary metabolism. To better understand the differentiation process, we constructed regulatory networks of transcription factors and SCW-related genes based on co-expression analyses. Accordingly, we found multiple regulatory modules that may underpin SCW deposition in sugarcane. Our results provide important insights and resources to identify biotechnological strategies for sugarcane biomass optimization.
This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) via the BIOEN Young Investigators Awards research grant (FAPESP no. 2015/02527-1). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Finance Code 001, by FAPESP (no. 2014/09623-6) and by FEDER/Agencia Estatal de Investigacio ìn with the Spanish Project AGL2017-83036R. IC thanks FAPESP for the SPRINT Project grant number 2016/50189-0. IC is indebted to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the research fellowship 302927/2018-2. MS was funded for a master’s fellowship (FAPESP no. 2015/18361-5). SF and AG were funded for a postdoctoral fellowship (FAPESP nos. 2016/06917-1 and 2019/13936-0). EF is indebted with CNPq for the research fellowship 303606/2017-7 and FAPESP no. 2016/17541-2. MB was supported by the National Institute of Science and Technology for Bioethanol (INCT-Bioethanol; FAPESP no. 2014/50884-5) and CNPq (465319/2014-9).