Fruit cell wall physiology and biochemistry to guide breeding the new generation of fruit genotypes (CASE)

Supervisors: Prof. Stephen C. Fry, Prof. Dušan Uhrín

Project Description:

Rationale. This project targets one of the BBSRC’s four Strategic Priority Areas: Agriculture and Food Security. It comprises novel research that is both of fundamental interest and has industrial applicability. The softening of ripening fruit involves dramatic changes in cell-wall structure. In many species, softening is important because it makes fruit pleasant to eat. On the other hand, excessive softening is detrimental, causing wastage on the supermarket shelf and making crops more vulnerable to pathogens. Slowing the softening process, e.g. in raspberries, would cause less waste when UK crops peak; imported crops, e.g. from Southern Europe and Morocco in winter, could  go further; and opportunities would be raised for summer UK exports. Slow-softening fruits would bring less disease and longer picking intervals.

Preliminary data from the applicants’ laboratories. Fry’s lab (Edinburgh) is elucidating novel mechanisms by which fruits soften. This work draws on many years’ experience of cell-wall biochemistry. Collaborators at Edward Vinson Ltd. (Kent), commercial fruit breeders, have a molecular breeding pipeline, e.g. in strawberry, raspberry and blackberry. We aim to link genetic markers (Edward Vinson) to physiological/biochemical processes (Edinburgh), benefiting future breeding efforts. Edward Vinson Ltd. is developing a molecular map for raspberry, so it will be possible to look for relevant genetic markers and use these in marker-assisted selection.

Proposed new research
Available genotypes differ in firmness, e.g. recently developed commercial genotypes versus ‘heritage’ varieties. We will explore the relationship between their genetics and their cell-wall processes. At the Edinburgh laboratory, the student will develop convenient new tools for screening cell-wall ‘softening markers’, including:

•    vitamin C secretion and turnover;
•    hydroxyl radicals non-enzymically attacking cell-wall polysaccharides in vivo;
•    solubilisation and partial degradation of pectic polysaccharides;
•    specific pectic enzyme activities and/or action in living fruit—
o    pectin methylesterase
o    rhamnogalacturonan lyase and pectate lyase (recent evidence suggests these enzymes contribute to softening)  
o    endopolygalacturonase
o    xyloglucan endotransglucosylase and endohydrolase (XTH)

Student’s role: initially working under close guidance. The student will explore the physiological/biochemical processes occurring in softening fruit cell walls. He/she will develop novel, simplified assays for these processes suitable for routine use by plant breeders. This study will employ chromatography and electrophoresis, with detailed practical guidance at Edinburgh. Training/experience will also be provided in preparing seminars, posters, reports and manuscripts; and undergraduate demonstrating.

Student’s role: subsequent opportunities for independent exploration. Later, depending on initial findings and personal interests, the student will be able to devise the best ways forward to fully characterise the processes. This may include in-vivo radiolabelling in Fry’s laboratory, and NMR spectroscopy and mass spectrometry in Edinburgh University’s Chemistry Department.

Industrial liaison. In the fruit breeding laboratory at Edward Vinson Ltd., the student will apply the novel assays he/she has developed, working closely with the molecular breeder and using his laboratory on-site. The student will also look at the novel softening markers in breeding material in the field, potentially linking field measurements of firmness with shelf-life. The period(s) of industrial liaison will provide insight into the opportunities and practicalities of commercial applied biology.

•    S.C. Fry (2017) Ripening. In Encyclopedia of Applied Plant Sciences, 2nd edition, Volume 1, pp. 323–334. Editors: B. Thomas, B.G. Murray, D.J. Murphy. Academic Press, Waltham, MA, USA. [PDF available from Prof. Fry].
•    O.B. Airianah, R.A.M. Vreeburg, S.C. Fry (2016) Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method. Annals of Botany, 117, 441–455,
•    R.A. Dewhirst, G.J.J. Clarkson, S.D. Rothwell, S.C. Fry (2017). Novel insights into ascorbate retention and degradation during the washing and post-harvest storage of spinach and other salad leaves. Food Chemistry, 233, 237–246,

If you wish to apply for this project, please go to this link.