Variation in DNA methylation patterns of grapevine somaclones (Vitis vinifera L.)

In traditional vine areas, the production should present a typicity that partly depends on the grapevine variety. Therefore, vine improvement is considered difficult because of the limited choice in the natural variability of the cultivars within the limits of their characteristics. A possibility to circumvent this problem is the use of somatic variability. In vitro somatic embryogenesis and organogenesis can lead to genotypic and phenotypic variations, described as somaclonal variation, that could be useful for the selection of improved grapevine genotypes.

In order to study tissue culture-induced variation of grapevine, we have analysed 78 somaclones obtained from somatic embryos of two distinct cultivars using molecular marker techniques. SSRs were only useful to verify the conservation of the microsatellite genotype between the somaclones and the respective mother clones. AFLP polymorphism between mother clones and somaclones was 1.3-2.8 times higher to that found between clones. However, a majority of the somaclones (45/78) exhibited only few changes. Seven and five somaclones of 'Chardonnay 96' and 'Syrah 174', respectively, which covered at least all polymorphic loci found in AFLP analysis were used for MSAP study. All of the 120 polymorphic fragments were found only in the somaclones. The percentage of full methylation at CCGG recognition sites was slightly higher in somaclones due to more polymorphic bands generated after cleavage by EcoRI/HpaII. Different digestion patterns revealed different methylation status, especially different levels of de-methylation, that are the consequence of the in vitro culture.

MSAP highlights DNA methylation variation in somaclones compared to mother clones and, therefore, is a powerful tool for genotypic characterisation of somatic embryo-derived grapevines. The detection of the same polymorphic bands in numerous somaclones of different cultivars suggests the possibility of hot spots of DNA methylation variation. SSR profiles of the 'Chardonnay' and 'Syrah' somaclones were the same as of the respective mother clones. The somaclones exhibited a higher AFLP variation than clones obtained via traditional clonal selection in the field. Therefore, somatic embryogenesis through in vitro culture technique could be useful for the selection of improved cultivars with subtle changes but conserving their main characteristics.