Investigating the role of the plant cell wall in crop freezing tolerance.

Freezing damage causes severe crop losses, particularly after unpredictably late or early frosts. The identification of plant traits that will lead to better frost tolerance is, therefore, of great importance to agriculture. Freezing causes damage to plant tissues through desiccation as water is drawn out of the cell when ice forms extracellularly and through rupture of cellular membranes during freeze-thaw cycles. Many temperate plants increase their freezing tolerance through cold acclimation, a program of transcriptional and metabolic adjustments triggered by low positive temperatures typical of those that occur during autumn. Transcriptomic studies indicate that cell wall remodelling may play a major role in cold acclimation, though little attention has been focused on this so far. This project seeks to understand how changes in the cell wall may improve the ability of plants to tolerate freezing temperatures. The lead supervisor's laboratory has recently identified a gene (SENSITIVE-TO-FREEZING-8; SFR8) that contributes to freezing tolerance by facilitating modifications to the plant cell wall. Through analysis of the sfr8 mutant and other cell wall mutants, this project aims to understand how dynamic changes in the composition, structure and physical properties of the cell wall may enhance freezing tolerance. Where genes of potential benefit during freezing are identified, these will be overexpressed in Arabidopsis and their effect on tolerance and cell wall properties analysed. The project will involve a multidisciplinary approach that examines the physical and biochemical nature of the cell wall and its relationship with ice nucleation and ice propagation around the cell. The project will also examine how the nature of the cell wall impacts upon cellular dehydration, one of the consequences of freezing damage. During the project the student will gain experience in a wide range of molecular, physiological, biochemical and imaging techniques. Freezing tolerance will be tested in mutant Arabidopsis plants with altered cell wall characteristics using quantitative electrolyte leakage assays, whilst cell wall elasticity will be measured in freezing-sensitive and tolerant plants using Atomic Force Microscopy. Ice nucleation and propagation within plant tissues will be tracked using infra-red video thermography. The student will also assess water use efficiency (WUE) in cell wall mutants and transgenic plants and stomatal conductance will be measured to build a picture of how the cell wall can influence guard cell closure and desiccation tolerance (Prof Anne Borland, Newcastle). A profile of cell wall compositional changes occurring in wild type plants during cold acclimation will be built up by characterising cold-upregulated cell wall genes using qRT-PCR and by using carbohydrate microarrays (Prof William Willats, Newcastle). This high-throughput method of obtaining comprehensive cell wall polysaccharide profiles uses panels of monoclonal antibodies to probe CW extracts. This multi-disciplinary training will provide an excellent platform for a wide range of future opportunities in scientific research or science-based careers.