Identification of nuclear localization signal in ASYMMETRIC LEAVES2-LIKE18/LATERAL ORGAN BOUNDARIES DOMAIN16 (ASL18/LBD16) from Arabidopsis

The ASYMMETRIC LEAVES2-LIKE/LATERAL ORGAN BOUNDARIES DOMAIN (ASL/LBD) gene family encodes proteins harboring a conserved plant-specific LOB domain. The LOB domain contains a four-Cys motif, a Gly–Ala–Ser (GAS) block, and a Leu-zipper-like coiled-coil motif. The ASL/LBD proteins are a unique class of transcription factors that play roles in lateral organ development of plants. Although the ASL/LBD proteins are localized in the nucleus, no consensus sequence for the nuclear localization of the ASL/LBD proteins could be found. In the present study, we determined the motifs responsible for the nuclear localization of ASL18/LBD16 by using protoplast transfection assays with a variety N- or C-terminal deletion polypeptide fragments and the polypeptides harboring changes in basic amino acids that are fused to enhanced green fluorescent protein. The results demonstrated that ASL18/LBD16 harbors two distinct domains comprising an atypical nuclear localization signal (NLS) with basic amino acid residues in the coiled-coil motif and a monopartite-like NLS in the C-terminal region for nuclear targeting.