Arabinose-rich polymers as an evolutionary strategy to plasticize resurrection plant cell walls against desiccation
A variety of Southern African resurrection plants were surveyed using high-throughput cell wall profiling tools. Species evaluated were the dicotyledons, Myrothamnus flabellifolia and Craterostigma plantagineum; the monocotyledons, Xerophyta viscosa, Xerophyta schlecterii, Xerophyta humilis and the resurrection grass Eragrostis nindensis, as well as a pteridophyte, the resurrection fern, Mohria caffrorum. Comparisons were made between hydrated and desiccated leaf and frond material, with respect to cell wall composition and polymer abundance, using monosaccharide composition analysis, FT-IR spectroscopy and comprehensive microarray polymer profiling in combination with multivariate data analysis. The data obtained suggest that three main functional strategies appear to have evolved to prepare plant cell walls for desiccation. Arabinan-rich pectin and arabinogalactan proteins are found in the resurrection fern M. caffrorum and the basal angiosperm M. flabellifolia where they appear to act as ‘pectic plasticizers’. Dicotyledons with pectin-rich walls, such as C. plantagineum, seem to use inducible mechanisms which consist of up-regulating wall proteins and osmoprotectants. The hemicellulose-rich walls of the grass-like Xerophyta spp. and the resurrection grass E. nindensis were found to contain highly arabinosylated xylans and arabinogalactan proteins. These data support a general mechanism of ‘plasticising’ the cell walls of resurrection plants to desiccation and implicate arabinose-rich polymers (pectin-arabinans, arabinogalactan proteins and arabinoxylans) as the major contributors in ensuring flexibility is maintained and rehydration is facilitated in these plants.
KeywordsArabinans Arabinogalactan proteins Arabinoxylans Cell wall profiling Resurrection plants
Alcohol insoluble residue
Comprehensive microarray polymer profiling
Carbohydrate binding module
Fourier transform-infrared spectroscopy
Our thanks go to Borakalalo National Park for donation of X. humilis, John and Sandy Burrows and Elizabeth Parker (Lydenberg district) for donation of C. wilmsii and X. viscosa, and Rupert and Tanya Baber (Waterberg district) for donation of M. flabellifolia, Professor Martin Kidd (Centre for Statistical Consultation, Stellenbosch University) is thanked for help and discussions on statistical data analysis. We would like to thank Jonatan Fangel (University of Copenhagen, Denmark) for help with the CoMPP figure artwork. The work was supported by grants to Jill Farrant from the Harry Oppenheimer Trust Foundation and University of Cape Town.
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