The invention relates to plant transcription factor polypeptides, polynucleotides that encode them, homologs from a variety of plant species, and methods of using the polynucleotides and polypeptides to produce transgenic plants having advantageous properties, including increased biomass or improved cold or other osmotic stress tolerance, as compared to wild-type or reference plants. The invention also pertains to expression systems that may be used to regulate these transcription factor polynucleotides, providing constitutive, transient, inducible and tissue-specific regulation.