This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

BackgroundPectins are plant cell wall polysaccharides that can be acetylated on C2 and/or C3 of galacturonic acid residues. The degree of acetylation of pectin can be modulated by pectin acetylesterase (EC 3.1.1.6, PAE). The function and structure of plant PAEs remain poorly understood and the role of the fine-tuning of pectin acetylation on cell wall properties has not yet been elucidated.ResultsIn the present study, a bioinformatic approach was used on 72 plant PAEs from 16 species among 611 plant PAEs available in plant genomic databases. An overview of plant PAE proteins, particularly Arabidopsis thaliana PAEs, based on phylogeny analysis, protein motif identification and modeled 3D structure is presented. A phylogenetic tree analysis using protein sequences clustered the plant PAEs into five clades. AtPAEs clustered in four clades in the plant kingdom PAE tree while they formed three clades when a phylogenetic tree was performed only on Arabidopsis proteins, due to isoform AtPAE9. Primitive plants that display a smaller number of PAEs clustered into two clades, while in higher plants, the presence of multiple members of PAE genes indicated a diversification of AtPAEs. 3D homology modeling of AtPAE8 from clade 2 with a human Notum protein showed an α/β hydrolase structure with the hallmark Ser-His-Asp of the active site. A 3D model of AtPAE4 from clade 1 and AtPAE10 from clade 3 showed a similar shape suggesting that the diversification of AtPAEs is unlikely to arise from the shape of the protein. Primary structure prediction analysis of AtPAEs showed a specific motif characteristic of each clade and identified one major group of AtPAEs with a signal peptide and one group without a signal peptide. A multiple sequence alignment of the putative plant PAEs revealed consensus sequences with important putative catalytic residues: Ser, Asp, His and a pectin binding site. Data mining of gene expression profiles of AtPAE revealed that genes from clade 2 including AtPAE7, AtPAE8 and AtPAE11, which are duplicated genes, are highly expressed during plant growth and development while AtPAEs without a signal peptide, including AtPAE2 and AtPAE4, are more regulated in response to plant environmental conditions.ConclusionBioinformatic analysis of plant, and particularly Arabidopsis, AtPAEs provides novel insights, including new motifs that could play a role in pectin binding and catalytic sites. The diversification of AtPAEs is likely to be related to neofunctionalization of some AtPAE genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3833-0) contains supplementary material, which is available to authorized users.

Early stages of plant development are highly susceptible to environmental cues, and seedlings have to develop sophisticated mechanisms to sense and respond to abiotic stresses. We have previously identified that abscisic acid (ABA), nitric oxide (NO) and modulation of nitrogen metabolism are involved in adaptive responses in Medicago truncatula seedlings under water deficit stress. Here, we investigated whether glutamate receptor-like channels (GLRs) played a role in the developmental physiological processes of Medicago seedlings during postgermination after a short-term water deficit stress. Twenty-nine independent MtGLR genes have been identified and then divided into four clades following a phylogenetic analysis; seventeen of them exhibited specific domains which are characteristic of animal ionotropic glutamate receptors. Under drought stress, ABA-induced NO accumulation was significantly reduced in presence of a GLR competitive antagonist, suggesting that this water deficit-induced endogenous NO production was mediated through a MtGLR-dependent pathway. Water deficitinduced inhibition of embryo axis elongation was strongly reduced whereas loss of water content was alleviated when MtGLRs were inhibited. These results suggest that glutamate receptors-like channels are required, through their involvement in NO production, in adaptive responses under short-term water-deficit stress during Medicago seedling establishment.