Compositions and methods for regulating expression of nucleotide sequences of interest in a plant are provided. Compositions include novel nucleic acid molecules, and variants and fragments thereof, for expression control elements isolated from the Lemnaceae ubiquitin, r-histone and chitinase genes. A method for expressing a nucleotide sequence of interest in a plant using the expression control elements disclosed herein is further provided. The method includes introducing into a plant or plant cell or nodule an expression construct comprising an expression control element of the present invention operably linked to a nucleotide sequence of interest. In particular, the compositions and methods find use in enhancing expression of nucleotide sequences of interest in duckweed. Also provided is a novel Lemnaceae signal peptide-encoding sequence and the signal peptide encoded thereby. Where an expression construct of the invention is designed to express a polypeptide of interest, this novel signal peptide-encoding sequence can be included within the expression construct of the invention to provide for extracellular secretion of the encoded polypeptide of interest.