The TPX-Like protein 3TPXL, but not TPX2, is the primary activator of {alpha} Aurora kinases and is essential for embryogenesis in Arabidopsis

Aurora kinases are key regulators of mitosis. Multicellular eukaryotes generally possess two functionally diverged types. In plants like Arabidopsis, these are termed α versus β Auroras. As the functional specification of Aurora kinases is determined by their specific interaction partners, we initiated interactomics analyses using both α Aurora kinases (AUR1 and AUR2). Proteomics results revealed the TPX2-Like proteins 2 and 3 (TPXL2/3) prominently associating with α Auroras, as did the conserved TPX2 to a lower degree. Like TPX2, TPXL2 and TPXL3 strongly activated AUR1 kinase but exhibited cell cycle-dependent localization differences on microtubule arrays. The separate functions of TPX2 and TPXL2/3 were also suggested by their different influences on AUR1 localization upon ectopic expressions. Furthermore, genetic analyses disclosed that TPXL3, but not TPX2 and TPXL2, acts non-redundantly to secure proper embryo development. In contrast to vertebrates, plants expanded the TPX2 family for both redundant and unique functions among its members.