Changes in the accumulation of alpha- and beta-tubulin during bud development in Vitis vinifera L.

Microtubules play important roles during growth and morphogenesis of plant cells. Multiple isoforms of alpha- and beta-tubulin accumulate in higher plant cells and originate either by transcription of different genes or by post-translational modifications. The use of different tubulin isoforms involves the binding of microtubules to different associated proteins and therefore generates microtubules with different organizations and functions. Tubulin isoforms are differentially expressed in vegetative and reproductive structures according to the developmental program of plants. In grapevine (Vitis vinifera L.), vegetative and reproductive structures appear on the same stem, making this plant species an excellent model to study the accumulation of tubulin isoforms. Proteins were extracted from grapevine samples (buds, leaves, flowers and tendrils) using an optimized extraction protocol, separated by two-dimensional electrophoresis and analyzed by immunoblot with anti-tubulin antibodies. We identified eight alpha-tubulin and seven beta-tubulin isoforms with pI around 4.8-5 that group into separate clusters. More acidic alpha-tubulin isoforms were detected in buds, while more basic alpha-isoforms were prevalently found in tendrils and flowers. Similarly, more acidic beta-tubulin isoforms were used in the bud stage while a basic beta-tubulin isoform was essentially used in leaves and two central beta-tubulin isoforms were characteristically used in tendrils and flowers. Acetylated alpha-tubulin was not detected in any sample while tyrosinated alpha-tubulin was essentially found in large latent buds and in bursting buds in association with a distinct subset of tubulin isoforms. The implication of these data on the use of different tubulin isoforms during grapevine development is discussed.