Fasciclin-like arabinogalactan proteins (FLAs) are a subclass of arabinogalactan proteins (AGPs) that have, in addition to predicted AGP-like glycosylated regions, putative cell adhesion domains known as fasciclin domains. In other eukaryotes (e.g. fruitfly [Drosophila melanogaster] and humans [Homo sapiens]), fasciclin domain-containing proteins are involved in cell adhesion. There are at least 21 FLAs in the annotated Arabidopsis genome. Despite the deduced proteins having low overall similarity, sequence analysis of the fasciclin domains in Arabidopsis FLAs identified two highly conserved regions that define this motif, suggesting that the cell adhesion function is conserved. We show that FLAs precipitate with β-glucosyl Yariv reagent, indicating that they share structural characteristics with AGPs. Fourteen of the FLA family members are predicted to be C-terminally substituted with a glycosylphosphatidylinositol anchor, a cleavable form of membrane anchor for proteins, indicating different FLAs may have different developmental roles. Publicly available microarray and expressed sequence tag data were used to select FLAs for further expression analysis. RNA gel blots for a number of FLAs indicate that they are likely to be important during plant development and in response to abiotic stress. FLAs 1,2, and 8 show a rapid decrease in mRNA abundance in response to the phytohormone abscisic acid. Also, the accumulation of FLA1 and FLA2 transcripts differs during callus and shoot development, indicating that the proteins may be significant in the process of competence acquisition and induction of shoot development.

Arabinogalactan proteins (AGPs) are extracellular hydroxyproline-rich proteoglycans implicated in plant growth and development. The protein backbones of AGPs are rich in proline/hydroxyproline, serine, alanine, and threonine. Most family members have less than 40% similarity; therefore, finding family members using Basic Local Alignment Search Tool searches is difficult. As part of our systematic analysis of AGP function in Arabidopsis, we wanted to make sure that we had identified most of the members of the gene family. We used the biased amino acid composition of AGPs to identify AGPs and arabinogalactan (AG) peptides in the Arabidopsis genome. Different criteria were used to identify the fasciclin-like AGPs. In total, we have identified 13 classical AGPs, 10 AG-peptides, three basic AGPs that include a short lysine-rich region, and 21 fasciclin-like AGPs. To streamline the analysis of genomic resources to assist in the planning of targeted experimental approaches, we have adopted a flow chart to maximize the information that can be obtained about each gene. One of the key steps is the reformatting of the Arabidopsis Functional Genomics Consortium microarray data. This customized software program makes it possible to view the ratio data for all Arabidopsis Functional Genomics Consortium experiments and as many genes as desired in a single spreadsheet. The results for reciprocal experiments are grouped to simplify analysis and candidate AGPs involved in development or biotic and abiotic stress responses are readily identified. The microarray data support the suggestion that different AGPs have different functions.

Arabinogalactan proteins (AGPs) are extracellular proteoglycans implicated in plant growth and development. We searched for classical AGPs in Arabidopsis by identifying expressed sequence tags based on the conserved domain structure of the predicted protein backbone. To confirm that these genes encoded bona fide AGPs, we purified native AGPs and then deglycosylated and deblocked them for N-terminal protein sequencing. In total, we identified 15 genes encoding the protein backbones of classical AGPs, including genes for AG peptides—AGPs with very short backbones (10 to 13 amino acid residues). Seven of the AGPs were verified as AGPs by protein sequencing. A gene encoding a putative cell adhesion molecule with AGP-like domains was also identified. This work provides a firm foundation for beginning functional analysis by using a genetic approach.

Plant cells are surrounded by highly dynamic cell walls that play important roles regulating aspects of plant development. Recent advances in visualization and measurement of cell wall properties have enabled accumulation of new data about wall architecture and biomechanics. This has resulted in greater understanding of the dynamics of cell wall deposition and remodeling. The cell wall is the first line of defense against different adverse abiotic and biotic environmental influences. Different abiotic stress conditions such as salinity, drought, and frost trigger production of Reactive Oxygen Species (ROS) which act as important signaling molecules in stress activated cellular responses. Detection of ROS by still-elusive receptors triggers numerous signaling events that result in production of different protective compounds or even cell death, but most notably in stress-induced cell wall remodeling. This is mediated by different plant hormones, of which the most studied are jasmonic acid and brassinosteroids. In this review we highlight key factors involved in sensing, signal transduction, and response(s) to abiotic stress and how these mechanisms are related to cell wall-associated stress acclimatization. ROS, plant hormones, cell wall remodeling enzymes and different wall mechanosensors act coordinately during abiotic stress, resulting in abiotic stress wall acclimatization, enabling plants to survive adverse environmental conditions.

Freezing triggers extracellular ice formation leading to cell dehydration and deformation during a freeze–thaw cycle. Many plant species increase their freezing tolerance during exposure to low, non‐freezing temperatures, a process termed cold acclimation. In addition, exposure to mild freezing temperatures after cold acclimation evokes a further increase in freezing tolerance (sub‐zero acclimation). Previous transcriptome and proteome analyses indicate that cell wall remodelling may be particularly important for sub‐zero acclimation. In the present study, we used a combination of immunohistochemical, chemical and spectroscopic analyses to characterize the cell walls of Arabidopsis thaliana and characterized a mutant in the XTH19 gene, encoding a xyloglucan endotransglucosylase/hydrolase (XTH). The mutant showed reduced freezing tolerance after both cold and sub‐zero acclimation, compared to the Col‐0 wild type, which was associated with differences in cell wall composition and structure. Most strikingly, immunohistochemistry in combination with 3D reconstruction of centres of rosette indicated that epitopes of the xyloglucan‐specific antibody LM25 were highly abundant in the vasculature of Col‐0 plants after sub‐zero acclimation but absent in the XTH19 mutant. Taken together, our data shed new light on the potential roles of cell wall remodelling for the increased freezing tolerance observed after low temperature acclimation.