Identification and characterization of three PeSHRs and one PeSCR involved in adventitious root development of Populus

The plant-specific GRAS family transcription factors, SHORT-ROOT (SHR) and SCARECROW (SCR), are key regulators of both the specification of the root stem cell niche and the differentiation potential of a subset of stem cells in the Arabidopsis root. Our previous microarray study indicated that SHR and SCR genes were involved in adventitious root development from hardwood cuttings in Populus. Here, we isolated and characterized three genes encoding SHR proteins and one gene encoding SCR proteins: PeSHR1, PeSHR2, PeSHR3 and PeSCR. Sequence and structure analysis showed that these proteins contained five well-conserved domains: leucine heptad repeat I (LHR I), the VHIID motif, leucine heptad repeat II (LHR II), the PFYRE motif, and the SAM motif. Temporal and spatial expression patterns of these genes were profiled during adventitious root development. Subcellular localization demonstrated that PeSHR1, PeSHR2 and PeSCR were localized to the nucleus, while PeSHR3 was localized to the cytoplasm. Finally, we adapted bimolecular fluorescence complementation to demonstrate that there was interaction between PeSHR1 and PeSCR. Collectively, these results contribute to improving our understanding of conserved and divergent aspects of SHR and SCR in various species.