Cell wall modulation by drought and elevated CO2 in sugarcane leaves

Abstract

Climate change poses significant challenges to global agriculture, with elevated atmospheric CO2 (eCO₂) concentrations and increased frequency of droughts affecting crop productivity. Understanding how economically important crops like sugarcane respond to these combined stresses is essential for developing resilient cultivars. This study explores the effects of eCO₂ and drought stress on sugarcane growth and cell wall composition. Sugarcane plants were cultivated under CO₂ treatments (390 ppm and 780 ppm) and subjected to drought stress. Leaf biomass, cell wall composition, and global transcriptome sequencing were analyzed. eCO₂ (780 ppm) significantly increased leaf biomass by 64%, attributed to enhanced photosynthesis and water-use efficiency. Conversely, drought reduced leaf biomass by 45%, highlighting sugarcane's sensitivity to water scarcity. When both conditions were combined, eCO₂ mitigated drought's negative impact, maintaining biomass at levels comparable to ambient conditions. Despite notable changes in biomass, cell wall biomass was only slightly affected. Under drought, a 14% reduction in cell wall biomass was observed alongside compositional changes, including reduced arabinosylation in glucuronoarabinoxylan (GAX). This alteration, supported by decreased xylan arabinosyl transferase (XAT) expression and reduced arabinose content, suggests stronger associations between GAX and cellulose, potentially enhancing drought tolerance by modifying cell wall rigidity and flexibility. Under eCO₂, cell wall composition was altered, with reductions in glucose and uronic acid in specific fractions, indicating decreased mixed-linkage glucan (MLG) and pectin. These changes likely increased cell wall flexibility, supporting rapid growth. Combined eCO₂ and drought treatments amplified specific modifications, such as enhanced fucosylation of xyloglucan (XG) and potential MLG expansion, both linked to stress adaptation. Overall, the findings underscore the critical role of cell wall plasticity in sugarcane's response to abiotic stress. While eCO₂ boosted growth and partially alleviated drought effects, structural changes in cell wall composition under these conditions further contribute to stress resilience, emphasizing the adaptive mechanisms of sugarcane to environmental challenges. This is the first report in which eCO₂, and drought are combined to evaluate the response of sugarcane to the impact of climate changes.

Keywords: NDP-sugar; abiotic stress; climate change; glycosyltransferases; grasses; transcriptome.

Figure 1

NDP-sugar synthesis and cell wall polysaccharide assembly pathway. Enzymes are indicated in orange. The NDP-sugar (green) pathway centers on UDP-glucose (UDP-Glc). Excluding GDP-fucose (GDP-Fuc) and GDP-mannose (GDP-Man), UDP-Glc is used to generate the other seven NDP-sugars: UDP-galactose (UDP-Gal), UDP-rhamnose (UDP-Rha), UDP-glucuronic acid (UDP-GlcA), UDP-galacturonic acid (UDP-GalA), UDP-apiose (UDP-Api), UDP-xylose (UDP-Xyl), UDP-arabinopyranose (UDP-Arap), and UDP-arabinofuranose (UDP-Araf). UDP-Glc can synthesize cellulose in the cell membrane or be sent to the Golgi apparatus along with the other NDP-sugars to synthesize pectins and hemicellulose (blue). For detail of the abbreviations and references, see Supplementary Data Sheet 1 and Supplementary Data 1 . Adapted from Pagliuso et al. (2022) and Verbančič et al. (2018).

Figure 2

Experimental design used to evaluate the response of sugarcane cell walls under different CO₂ concentrations and watering conditions. Sugarcane plants (var. SP80-3280) were grown in Open-Top Chambers (OTCs) under four treatment conditions: ambient CO₂ ([aCO₂], 390 ppm) with adequate watering, elevated CO₂ ([eCO₂], 780 ppm) with adequate watering, ambient CO₂ with drought stress [Dro], and elevated CO₂ with drought stress [eCO₂+Dro]. Growth parameters, cell wall fractionation, and transcriptome analysis were performed to assess the impact of these conditions on the sugarcane cell wall.

Figure 3

Expression patterns of 32 gene families related to the synthesis of cell wall polysaccharides. Experimental treatments: aCO₂ (ambient CO₂, 390 ppm), eCO₂ (elevated CO₂, 780 ppm), Dro (drought), and eCO₂+Dro (elevated CO₂, 780 ppm, combined with drought).

Figure 4

Differential gene expression of cell wall polysaccharide synthesis families in sugarcane SP80-3280 leaves under varying CO₂ and watering conditions. Differences were identified when any treatment significantly differed from the control condition, with further comparisons among all treatments detailed in Supplemental Data Sheet 4 . Significant differences (p< 0.05) were determined using a Generalized Linear Model followed by Tukey's test, with different letters indicating significance. Expression values are presented as log₁₀ counts per million (CPM), normalized for each sequence. Treatments include aCO₂ (ambient CO₂, 390 ppm), eCO₂ (elevated CO₂, 780 ppm), Dro (drought), and eCO₂+Dro (elevated CO₂, 780 ppm, combined with drought). SUS, sucrose synthase; PGI, phosphoglucose isomerase; INV, invertase; HXK, hexokinase; RHM, rhamnose biosynthesis enzyme; UXS, UDP-glucuronate decarboxylase; GALE, UDP-galactose-4-epimerase; UAM, UDP-arabinopyranose mutase; CesA, cellulose synthase; CslF-H, cellulose synthase-like F-H; XAT, xylan arabinosyltransferase; GAUT, α-galacturonosyltransferase.

Figure 5

Leaves biomass (dry mass) weight in sugarcane plants grown under different CO₂ concentrations and watering conditions. Bars represent the mean ± standard error (n = 4). Different letters indicate significant differences (p< 0.05), determined by one-way ANOVA and Tukey's test. aCO₂, ambient CO₂ (390 ppm); eCO₂, elevated CO₂ (780 ppm); Dro, drought; eCO₂+Dro, elevated CO₂ (780 ppm) combined with drought.

Figure 6

Sugarcane carbohydrate composition of plants grown in different CO₂ concentrations and watering conditions. (A) Alcohol soluble compounds (ASC), starch, and cell wall proportions. (B) Yield of cell wall sequential fractionation. (C) Cell wall degradation along sequential extraction. The results were expressed in relative form. Bars are represented by mean ± standard error (n = 4). Different letters indicate significant differences (p< 0.05), determined by one-way ANOVA and Tukey's test. aCO₂, ambient CO₂ (390 ppm); eCO₂, elevated CO₂ (780 ppm); Dro, drought; eCO₂+Dro, elevated CO₂ (780 ppm) combined with drought; AmnOx, ammonium oxalate fraction; NaClO₂, sodium chlorite fraction; 4M NaOH, sodium hydroxide fraction; MLG, mixed-linked-glucan; GAX, glucuronoarabinoxylan; and XG, xyloglucan.

Figure 7

Lignin relative content in sugarcane cell walls under different CO₂ concentrations and drought. Bars represented by mean ± standard error (n = 4). Different letters indicate significant differences (p< 0.05), determined by one-way ANOVA and Tukey's test. aCO₂, ambient CO₂ (390 ppm); eCO₂, elevated CO₂ (780 ppm); Dro, drought; eCO₂+Dro, elevated CO₂ (780 ppm) combined with drought.

Figure 8

Uronic acid levels in AIR and different fractions of Cell Wall in sugarcane leaves. Bars represented by mean ± standard error (n = 4). Different letters indicate significant differences (p< 0.05), determined by one-way ANOVA and Tukey's test. aCO₂ = ambient CO₂ (390 ppm), eCO₂= elevated CO₂ (780 ppm), Dro = drought, eCO₂+Dro = elevated CO₂ (780 ppm) combined with drought. AIR, Alcohol Insoluble Residue (intact cell wall); AmnOx, ammonium oxalate fraction; NaClO₂, sodium chlorite fraction; 4M NaOH, sodium hydroxide fraction.

Figure 9

Summary of results and proposed interpretations (black rectangle) of the impact of isolated and combined elevated CO₂ (eCO₂) and drought on cell wall synthesis and composition in sugarcane SP80-3280 leaves. UXS, UDP-glucuronate decarboxylase; GalE, UDP-galactose-4-epimerase; UAM, UDP-arabinopyranose mutase; CesA, cellulose synthase; XAT, xylan arabinosyltransferase; GAX, glucuronoarabinoxylan; HG, homogalacturonan; MLG, mixed-glucan; RG, rhamnogalacturonan; XG, xyloglucan.