Lupinus albus gamma-tubulin: mRNA and protein accumulation during development and in response to darkness.

We have isolated a genomic DNA fragment encoding a gamma-tubulin in white lupin ( Lupinus albus L.). The predicted polypeptide encoded by the La-TubG1 gene possesses between 91 and 95% identity with other higher-plant gamma-tubulins. The mRNA and protein level of lupin gamma-tubulin is highly correlated with beta-tubulin as well as with the growth rate of the tissue. Both La-TubG1 transcript and gamma-tubulin protein expression levels are down-regulated in the embryonic axis of dry seeds as compared with the embryonic axis of germinated seeds. In 7-day-old seedlings, the La-TubG1 gene is ubiquitously expressed, with the highest level found in immature leaves. In contrast, La-TubG1 gene expression is down-regulated in mature leaves. The gamma-tubulin protein level follows a similar age-dependent accumulation, decreasing during leaf development. The expression of the gamma-tubulin gene in the hypocotyl is down-regulated by light. Nevertheless, the protein levels were not significantly altered by light, suggesting that gamma-tubulin accumulation might be controlled at both transcriptional and protein levels. Immunocytochemistry studies showed that lupin gamma-tubulin displays the localization observed in most plant microtubule arrays, corroborating a functional conservation in different species.