Abstract
The transition of stem cells from self-renewal into differentiation is tightly regulated to assure proper development of the organism. Arabidopsis MINIYO (IYO) and its mammalian orthologue RNA polymerase II associated protein 1 (RPAP1) are essential factors for initiating stem cell differentiation in plants and animals. Moreover, there is evidence suggesting that the translocation of IYO and RPAP1 from the cytosol into the nucleus functions as a molecular switch to initiate this cell fate transition. Identifying the determinants of IYO subcellular localization would allow testing if, indeed, nuclear IYO migration triggers cell differentiation and could provide tools to control this crucial developmental transition. Through transient and stable expression assays in Nicotiana benthamiana and Arabidopsis thaliana, we demonstrate that IYO contains two nuclear localization signals (NLSs), located at the N- and C-terminus of the protein, which mediate the interaction with the NLS-receptor IMPA4 and the import of the protein into the nucleus. Interestingly, IYO also interacts with GPN GTPases, which are involved in selective nuclear import of RNA polymerase II. This interaction is prevented when the G1 motif in GPN1 is mutated, suggesting that IYO binds specifically to the nucleotide-bound form of GPN1. In contrast, deleting the NLSs in IYO does not prevent the interaction with GPN1, but it interferes with import of GPN1 into the nucleus, indicating that IYO and GPN1 are co-transported as a complex that requires the IYO NLSs for import. This work unveils key domains and factors involved in IYO nuclear import, which may prove instrumental to determine how IYO and RPAP1 control stem cell differentiation.
Highlights
Arabidopsis MINIYO (IYO) is a key pro-differentiation factor whose migration from the cytosol into the nucleus coincides with the onset of stem cell differentiation (Sanmartin et al, 2011; Sanmartin et al, 2012; Muñoz et al, 2017)
Despite the evidence that IYO/RNA polymerase II associated protein 1 (RPAP1) subcellular distribution is key for determining stem cell fate in plant and animals (Muñoz et al, 2017; Lynch et al, 2018), the domains responsible for translocation into the nucleus and the possible mechanisms involved in nuclear import were unknown
The work presented here reveals the primary role of NLS located between positions and 259 (NLSA) in nuclear import of IYO
Summary
Arabidopsis MINIYO (IYO) is a key pro-differentiation factor whose migration from the cytosol into the nucleus coincides with the onset of stem cell differentiation (Sanmartin et al, 2011; Sanmartin et al, 2012; Muñoz et al, 2017). Nuclear protein import requires in many cases active transport mechanisms, which are dependent on the presence of a specific nuclear localization signals (NLS) in the sequence of the proteins to be imported (Dingwall and Laskey, 1991). There is a third type of non-classical NLS, found only in yeast and plant proteins, whose consensus sequence (KIPIK) is rich in lysine (Hicks et al, 1995). Canonical transport into the nucleus mediated by NLS-type signals occurs in a two-step process: in the cytoplasm, proteins with an NLS interact through this domain with the importin-α subunit of nuclear import receptors. The importin-β subunit of the receptor interacts with nucleoporins to facilitate transport of the receptor-cargo complex across the nuclear pore (Smith et al, 1997; Macara, 2001). Nuclear transport rate is dependent on the affinity of importins for the cargo NLS and on the importin availability (Dingwall and Laskey, 1991; Riddick and Macara, 2005)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
