Molecular control of grapevine flowering

Identification and functional characterisation of genes involved in floral initiation and development

Supervisors: Dr Mark Thomas (08 8303 8624)
Location: Adelaide
Financial support: To be confirmed

The yield from a vineyard fluctuates significantly (15% -30%) from year to year and is largely determined by the fruitfulness of a vine. However this process is not well understood for grapevine. Fruitfulness is a combination of factors: number of inflorescences per vine, flower number per inflorescence, fruit set and berry development. The process occurs over two seasons with floral initiation occurring in the first season in latent buds followed in the second season after bud burst by inflorescence growth and fruit growth. Management techniques such as pruning level can have an effect on yield but it is largely the interaction of environmental conditions and the genes in the plant that determine the degree of fruitfulness. It is known that inflorescence number per vine is the main component of yield and this is determined by the success of floral initiation.

To gain a better understanding of grapevine fruitfulness we have isolated key genes involved in grapevine flowering during latent bud development and after bud burst.  Identifying the key genes in this genetic network and determine how these genes are influenced by the environment are essential first steps in understanding the in planta control of fruitfulness. A grapevine gene flowering model has been developed and fourteen flowering pathway genes were separated into 3 groups based on their roles and include:  flowering time genes, inflorescence and floral meristem identity genes, and floral organ identity genes. Evaluation of some of these grapevine genes demonstrated that they either promoted or delayed flowering in other species. A gene involved in grapevine flowering was identified and was found to be associated with the conversion of tendrils to bunches of grapes.

Aims: This project will investigate the genes responsible for the early events of floral initiation. Gene information from flowering models developed for Arabidopsis will be utilised to clone the corresponding genes from grapevine and the function of these genes investigated. How the environment influences gene expression will also be investigated.

Experimental approach: New genes will be identified using bioinformatic mining of microarray data, EST and genomic sequence databases. Identified genes will be isolated from existing cDNA or genomic libraries and expression patterns investigated by real-time PCR and RNA in situ methods. Transgenic approaches will be used to investigate gene function. Plants grown under controlled conditions in growth rooms will be used to investigate the effect of the environment on the expression of genes involved in floral initiation.

References:

• Boss PK, Thomas MR (2002) Association of dwarfism and floral induction with a grape 'green revolution' mutation. Nature 416: 847- 850
• Boss PK, Buckeridge EJ, Poole A, Thomas MR (2003) New insights into grapevine flowering.  Functional Plant Biology 30: 593-606
• Boss PK, Sreekantan L, Thomas MR (2006) A grapevine TFL1 homologue can delay flowering and alter floral development when overexpressed in heterologous species.  Functional Plant Biology 33: 31-41
• Sreekantan L, Torregrosa L, Fernandez L, Thomas MR (2006) VvMADS9, a class B MADS-box gene involved in grapevine flowering, shows different expression patterns in mutants with abnormal petal and stamen structures.  Functional Plant Biology 33: 877-88