TPX2 Protein of Arabidopsis Activates Aurora Kinase 1, But Not Aurora Kinase 3 In Vitro

Aurora kinases are involved in various mitotic events, including chromosome segregation and bipolar mitotic spindle assembly. In animals, Aurora A is activated and protected by microtubule-associated protein TPX2. Such role in plants is not known. Here, we have assessed the ability of TPX2 of Arabidopsis to regulate Aurora family members in vitro. AtTPX2 acts as substrate as well as activator of AtAurora1, but not AtAurora3. Truncated version of AtTPX2 lacking the Aurora binding domain is unable to activate the kinases; however, it is still phosphorylated. AtTPX2-induced activation of AtAurora1 results in a dramatically increased phosphorylation level of downstream targets, particularly histone H3. The differences in the activation mechanism of AtAurora1 and 3 point to a specific regulation of both kinases, which may play an important role in cell cycle regulation and signaling cascade transduction in plants.