The nuclear envelope – which comprises an outer and inner nuclear membrane (ONM and INM) – separates the cytoplasm and the nucleus. Proteins at the INM are involved in numerous nuclear and cellular processes, such as transcription, chromatin organization and mechanotransduction. In contrast to what is seen in animal and yeast cells, the composition of the nuclear envelope proteome and the mechanisms that target proteins to the INM are largely unknown in plants. In their research article, Iris Meier and colleagues (Groves et al., 2019) tested whether INM targeting through protein import by means of a nuclear localization signal is conserved in plant cells. They tested whether several ER membrane proteins fused to mono- or bi-partite NLSs could relocate to the plant cell INM, and found that NLS addition is sufficient for INM targeting. Interestingly, a yeast INM protein fragment is enriched at the plant INM, but less so than its full-length version, suggesting differential targeting of this INM protein by yeast and plant cells. Taken together, this work suggests that there is an NLS-dependent INM-targeting pathway in plant cells. The different protein sizes and conformations tested in this work suggest limitations to INM targeting may be more relaxed in plants than in other systems. The protein targeting rules and constructs the authors provide could be harnessed to address future questions on the functional aspects of the plant nuclear envelope.
