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Traveling transcription factors

I always thought that transcription factors stay in the cells where they are expressed and control transcription of their target genes. A recent report in Genes Development talks about a transcription factor in plant cells that goes from cell to cell. Quite interesting.

KN1 is a transcription factor that moves from cell to cell in order to regulate, among other things, stem cell identity in the shoot apical meristem of maize. Another transcription factor, GL1, prefers to stay in its home cell, where it regulates the formation of tiny hairs (trichomes) in the leaf epidermis of Arabidopsis. Whether intercellular transport of KN1 is regulated is addressed by Kim et al. By making a chimeric construct of KN1 with GL1, the authors determined which portions of KN1 could drive intercellular transport of misexpressed GL1 and thus rescue trichome formation. A GL1-KN1 fusion using only the C-terminal portion of KN1 supported rescue through intercellular transport, whereas the fusion using the N-terminal portion of KN1 did not. The homeodomain included in that C-terminal portion of KN1 turned out to be critical. Both the mRNA and the KN1 homeodomain protein seem to be required for intercellular trafficking. Thus, the KN1 homeodomain is required to transport both itself and its mRNA through plasmodesmatal channels.

Genes Dev. 10.1101/gad.332805 (2005).