Analysis of the genetic variation of flowering time genes and their control network in grapevine
Vitis vinifera (2n = 38) is the only grape native to Europe.It’s a woody perennial liana climbing up to the top of supporting trees in its natural habitat. Grapevine plants flower usually first in the third year after planting, with inflorescences forming out of tendrils dur ing summer but resting in the buds throughout autumn and winter until blossom in the next spring. The wild vine V. v. subspec. sylvestris
is dioecious with individual male and female plants, while most of the cultivated subspecies show hermaphroditic flowers.
Although flowering time control (FTC), time of ripening and also the control of the number of inflorescences formed is of high biological relevance in grapevine, our current knowledge about the genetic and environmental factors that determine these traits is still very limited. Several genes with a putative function in FTC have been identified based on data from the model system Arabidopsis. However, control of flowering in grapevine as a woody perennial shows significant differences to the Arabidopsis model system. For example, neither photoperiod nor vernalization seem to have an impact on flower promotion, and the plant hormone gibberellic acid has been shown to have a complementary effect compared with the one described for Arabidopsis. The project will improve our understanding of how flowering in grapevine as a woody perennial species is regulated and which genes are involved.
These are the major questions to be addressed:
- What are the factors within the FTC network that cause grapevines to flower early or late?
- What determines the basal buds to flower while the upper buds form tendrils?
In two complementary approaches we will analyse the genes involved in flowering time control in grapevine:
(1) Progeny from a cross which segregate for early and late flowering will be analysed for QTLs for flowering time control. In such QTL regions candidate genes will be identified based on the grapevine reference genome sequence.
(2) In a comparative genetics approach candidate genes for flowering time control known from model systems like Arabidopsis will be used to exploit the grapevine genome for homologues. Since grapevine is extremely heterozygous, haplotypes for these candidate genes will be identified by 454 amplicon-sequencing in a set of genetically diverse genotypes showing variation in flowering time. The results will be used to associate grapevine haplotypes with early or late flowering phenotypes, respectively.
(3) At the functional level RNA-seq and qRT-PCR experiments will be performed to monitor the gene expression of candidate genes in the parents and selected genotypes of the F1 progeny. The data will show which genes are most relevant for determining flowering time control between early and late genotypes. Comparison with results from other projects of the SSP will allow to deduce an action scheme of how flowering time is controlled in grapevine.
Fechter I, Hausmann L, Zyprian E, Daum M, Holtgräwe D, Weisshaar B, Töpfer R (2014). QTL analysis of flowering time and ripening traits suggest an impact of a genomic region on linkage group 1 in Vitis. Theoretical and Applied Genetics, Theor Appl Genet. 2014; 127(9): 1857–1872, doi: 10.1007/s00122-014-2310-2