Defining the role of three plant hormones during wine grape berry ripening

Supervisors: Dr Christopher Davies (08 8303 8628)
Location: Adelaide
Financial support: To be confirmed

This project forms part of a larger program of research aimed at better understanding grape berry development and in particular the involvement of hormones during berry ripening. Plant hormones control plant development through inducing coordinated changes in gene expression and are important in most developmental processes. In grape berries we have evidence that ripening is under the control of endogenous hormones. Both the timing of the initiation, and the rate of ripening, are crucial to the date of commercial ripeness and most likely also to berry composition. Three plant hormones (abscisic acid (ABA), ethylene and brassinosteroids (BRs)) have been identified as involved in ripening but the mechanism of their action, their relative influence and their potential usefulness in manipulating this process are yet to be well characterised. A better understanding of the mechanism of action of these hormones and how they interact to control ripening offers the possibility for manipulating berry ripening to advantage. Control over the timing of harvest through manipulating ripening may improve yield and quality, and reduce loss in cooler climates and allow greater flexibility in winery scheduling during winemaking. The manipulation of ripening via hormones may also increase the synchronicity of ripening and provide flexibility in berry composition and therefore wine style by altering the balance of berry metabolism.

Aims: The overall project aim is to gain a better understanding of the action of ABA, ethylene and BRs on grape berry ripening. This will occur through gaining knowledge of the mechanism of hormone action, the changes in gene expression they induce, the potential interactions between them and the effects they exert on berry development and metabolism.

Experimental approach: Field, glasshouse and laboratory experiments will be used to further elucidate the action of the three hormones discussed above on grape berry ripening. These hormones (and inhibitors of their biosynthesis and perception) will be used in experiments on tissue culture cells, whole berries and in field experiments on entire bunches to identify their effect on gene expression and metabolism. Gene expression changes will be measured techniques such as real-time PCR and microarray analysis. Differential application of hormones and the use of inhibitors of hormone synthesis and action will be used to investigate the possible interaction between the hormone candidates. Changes in berry metabolism will be measured by biochemical analysis and related to gene expression changes and possible gene function to form a more holistic picture of hormone action during berry development.

References:

• Davies C et al. (1997) Treatment of grape berries, a nonclimacteric fruit with a synthetic auxin, retards ripening and alters the expression of developmentally regulated genes. Plant Physiology 115: 1155-1161.
• Davies C and Robinson SP (2000) Differential screening indicates a dramatic change in mRNA profiles during grape berry ripening. Cloning and characterisation of cDNAs encoding putative cell wall and stress response proteins. Plant Physiology 122: 803-812.
• Chervin C et al. (2004). Ethylene seems required for the berry development and ripening in grape, a non-climacteric fruit. Plant Sci. 167: 1301-1305.