Cell Wall Compositions of Sorghum bicolor Leaves and Roots Remain Relatively Constant Under Drought Conditions.

Tess Scavuzzo-Duggan,Peggy Lemaux,Nelle Varoquaux,Robert Hutmacher,John P Vogel,Michael Belcher,Henrik V Scheller,Elizabeth Purdom,Devin Coleman-Derr,Jasmine Ortega,Mary Madera,Jeffery Dahlberg

doi:10.3389/fpls.2021.747225

Abstract

Renewable fuels are needed to replace fossil fuels in the immediate future. Lignocellulosic bioenergy crops provide a renewable alternative that sequesters atmospheric carbon. To prevent displacement of food crops, it would be advantageous to grow biofuel crops on marginal lands. These lands will likely face more frequent and extreme drought conditions than conventional agricultural land, so it is crucial to see how proposed bioenergy crops fare under these conditions and how that may affect lignocellulosic biomass composition and saccharification properties. We found that while drought impacts the plant cell wall of Sorghum bicolor differently according to tissue and timing of drought induction, drought-induced cell wall compositional modifications are relatively minor and produce no negative effect on biomass conversion. This contrasts with the cell wall-related transcriptome, which had a varied range of highly variable genes (HVGs) within four cell wall-related GO categories, depending on the tissues surveyed and time of drought induction. Further, many HVGs had expression changes in which putative impacts were not seen in the physical cell wall or which were in opposition to their putative impacts. Interestingly, most pre-flowering drought-induced cell wall changes occurred in the leaf, with matrix and lignin compositional changes that did not persist after recovery from drought. Most measurable physical post-flowering cell wall changes occurred in the root, affecting mainly polysaccharide composition and cross-linking. This study couples transcriptomics to cell wall chemical analyses of a C4 grass experiencing progressive and differing drought stresses in the field. As such, we can analyze the cell wall-specific response to agriculturally relevant drought stresses on the transcriptomic level and see whether those changes translate to compositional or biomass conversion differences. Our results bolster the conclusion that drought stress does not substantially affect the cell wall composition of specific aerial and subterranean biomass nor impede enzymatic hydrolysis of leaf biomass, a positive result for biorefinery processes. Coupled with previously reported results on the root microbiome and rhizosphere and whole transcriptome analyses of this study, we can formulate and test hypotheses on individual gene candidates’ function in mediating drought stress in the grass cell wall, as demonstrated in sorghum.

Highlights

As fossil fuel resources decline and usage continues to have adverse effects on global climate, it is crucial to develop alternative fuel sources to supply energy demand
While there have been several studies detailing the transcriptomic differences of drought-stressed grasses (Buchanan et al., 2005; Dugas et al., 2011; Lenk et al., 2019), and several studies detailing cell wall changes in grasses affected by drought stress (Vincent et al., 2005; Emerson et al., 2014; Ottaiano et al., 2017; van der Weijde et al., 2017; El Hage et al., 2018; Hoover et al., 2018), this is the first study to detail the cell wall-related transcriptomic differences and the cell wall differences in a drought-tolerant C4 grass affected by several different drought stresses in the field
As with previous transcriptomic studies (Buchanan et al., 2005; Spollen et al., 2008; Dugas et al., 2011; Le Gall et al., 2015; Tenhaken, 2015; Rasheed et al., 2016; Lenk et al., 2019; Varoquaux et al., 2019), we see that gene ontology (GO) terms and categories relating to the cell wall are significantly affected by drought stress, the transcriptomic response to drought stress is large in sorghum, with more than 40% of expressed genes experiencing an effect on expression patterns relative to wellwatered conditions (Varoquaux et al., 2019)

Summary

Introduction

As fossil fuel resources decline and usage continues to have adverse effects on global climate, it is crucial to develop alternative fuel sources to supply energy demand. Recent studies have demonstrated that the use of lignocellulosic biofuels has the potential to sequester carbon from the atmosphere by increasing soil organic carbon, which may help mitigate increased carbon release to the atmosphere (Vanholme et al, 2013; Taptich et al, 2018; Wu et al, 2018). Despite these advantages, lignocellulosic biofuels have several requirements to meet before they can be considered competitive with petroleum-based fuels. In addition to high biomass yields, the lignocellulosic properties of the feedstocks would ideally not be altered by drought (Somerville et al, 2010; van der Weijde et al, 2013; Vanholme et al, 2013)

Methods

Results

Discussion

Conclusion