Identification of candidate genes involved in phylloxera resistance in grapevine rootstocks.

The grapevine rootstock cultivar 'Borner' is resistant against phylloxera (Daktulosphaira vitifoliae Fitch), one of the major pests in viticulture. In contrast to tolerant or sensitive rootstocks, 'Borner' roots react to a phylloxera attack with a hypersensitive response exhibiting features of programmed cell death. Using cDNA subtraction in 'Borner' roots induced by IAA (a cecidogenic component of the Phylloxera saliva) and analysed at different times post induction, differential expression of several genes putatively involved in phylloxera resistance was established. Furthermore, DNA microarray analysis of subtracted and unsubtracted cDNA populations using a heterologous system (Arabidopsis thaliana) yielded more than 600 genes differentially expressed at various times after induction. Recently, a quantitative analysis of differentially expressed genes was initiated using an advanced microarray techniques ('Geniom one', febit AG) with oligo-DNA custom chips harbouring more than 450 relevant entries of the Vitis UniGen databank and a number of pathogen response-related genes of A. thaliana. Using this method, 25 up-and 7 down-regulated genes could be identified in 'Borner'. Differential expression of several of these candidate genes has been validated by quantitative RT-PCR.