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

We have isolated a genomic DNA fragment encoding a γ-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 γ-tubulins. The mRNA and protein level of lupin γ-tubulin is highly correlated with β-tubulin as well as with the growth rate of the tissue. Both La-TubG1 transcript and γ-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 γ-tubulin protein level follows a similar age-dependent accumulation, decreasing during leaf development. The expression of the γ-tubulin gene in the hypocotyl is down-regulated by light. Nevertheless, the protein levels were not significantly altered by light, suggesting that γ-tubulin accumulation might be controlled at both transcriptional and protein levels. Immunocytochemistry studies showed that lupin γ-tubulin displays the localization observed in most plant microtubule arrays, corroborating a functional conservation in different species. [ABSTRACT FROM AUTHOR]