Molecular characterization and expression analysis of the Rab GTPase family in Vitis vinifera reveal the specific expression of a VvRabA protein

As a first step to investigate whether Rab GTPases are involved in grape berry development, the Vitis vinifera EST and gene databases were searched for members of the VvRab family. The grapevine genome was found to contain 26 VvRabs that could be distributed into all of the eight groups described in the literature for model plants. Genetic mapping was successfully performed; VvRabs were mostly located on independent chromosomes, apart from eight that were located on the as yet unassigned portions of the genome clustered in the ChrUn_Random chromosome. Conserved and divergent regions between VvRab protein sequences were identified. Transcript expression of 11 VvRabs was analysed by real-time quantitative RT-PCR. Except for VvRabA5b, transcript expression was detected, in general, in all the organs investigated, but with different patterns. In grape berries, VvRab transcripts were expressed at all stages of fruit development, with different profiles, except in the case of members of the A family which displayed generally similar patterns. The response to growth regulators in cell cultures was generally specific to each VvRab, with a differential pattern of expression for ethylene, auxin, and abscisic acid according to the VvRab. Interestingly, and unexpectedly considering transcript expression, western blotting using a monoclonal antibody raised against AtRabA5c (ARA4) showed a specific expression in the exocarp of ripe grape berries, in all seven red and white berry varieties tested. By contrast, no expression was detected in any of the other organs or tissues investigated. This paper contains the first description of Rab GTPases in V. vinifera. The involvement of a specific VvRab in grape berry late development and the potential role of this Rab GTPase are discussed in relation to literature data.