Unveiling the Movement of RanBP1 During the Cell Cycle and Its Interaction with a Cyclin-Dependent Kinase (CDK) in Plants

In the Nicotiana tabacum flower development study, we identified SCI1(Stigma/style Cell-cycle Inhibitor 1), a regulator of cell proliferation. SCI1 interacts withNtCDKG;2 (N. tabacum Cyclin-Dependent Kinase G;2), a homolog of human CDK11, whichis responsible for RanGTP-dependent microtubule stabilization, regulating spindle assemblyrate. In a Y2H screening of a cDNA library using NtCDKG;2 as bait, a RanBP1(Ran-Binding Protein 1) was revealed as its interaction partner. RanBP1 is an essentialregulatory protein of the RanGTPase system, contributing to the formation of the Rangradient, which modulates different important cellular processes. RanBP1 is crucial in thenuclear import/export machinery during interphase and spindle checkpoint formationduring cell division. These processes are well studied in animals, but very little is knownabout them in plants. We confirmed NtCDKG;2 and NtRanBP1 interaction by pairwiseY2H and characterized the localization of both proteins during plant cell division. Wedemonstrated the presence of NtRanBP1 in the cytoplasm during interphase and its nucleararrest at mitosis onset. Meanwhile, we showed that NtCDKG;2 is localized in the mitoticspindle during cell division, indicating an analogous function to the human CDK11. Wepropose that the phosphorylation of the nuclear export signal at RanBP1 by NtCDKG;2may be responsible for the reported nuclear arrest.