Identification of potential cargo proteins of transportin protein AtTRN1 in Arabidopsis thaliana.

KEY MESSAGE: We identified 23 novel proteins that can interact with At TRN1. These proteins are potential candidates of At TRN1 cargo proteins, which will facilitate our comprehending of At TRN1 functions in Arabidopsis. Tranportin 1 (TRN1) carries out the nucleo-cytoplasmic transport of many proteins, thereby ensuring that each of them is delivered to the right compartment for its proper function. These cargo proteins involved in lots of important processes, such as alternative pre-mRNA splicing, transcriptional regulation, and protein translation. Current understanding of cargo proteins transported by Arabidopsis thaliana transportin 1 (AtTRN1) is limited. Here, first we employed the yeast two-hybrid (Y2H) screening to identify proteins that can interact with AtTRN1 in Arabidopsis, and 12 novel proteins were found. Searching for PY-NLS motif in these 12 proteins suggested that no typical PY-NLS motif was present. We next investigated the specific motifs that will mediate the interactions in these sequences, and found that thirteen truncated fragments interacted with AtTRN1, containing 8 acidic and 5 basic fragments, respectively. We also searched the Arabidopsis proteome for homologs of cargo proteins of yeast Kapl04p and mammalian Kapβ2, and PY-NLS motif-containing proteins. Among these proteins, 11 were identified to interact with AtTRN1. The interactions between all the 23 proteins and AtTRN1 were confirmed by both Y2H and bimolecular fluorescence complementation (BiFC) assays. Our results show that AtTRN1 recognizes a broad spectrum of proteins having diverse functions, which will potentially be the cargoes of AtTRN1. Taken together, these results demonstrate the feasibility and potential power of these methods to identify cargo proteins of AtTRN1, and represent a primary and significant step in interpretation of AtTRN1 functionalities.