Compositions and methods for improving plant growth are provided herein. Disclosed herein are polypeptides encompassing m-type thioredoxin proteins, and polynucleotides encoding m-type thioredoxin proteins, wherein the thioredoxin protein-encoding sequence is expressed from mesophyll-preferred promoters. Also provided herein are expression constructs for expressing genes of interest whose expression may improve agronomic properties including but not limited to crop yield, biotic and abiotic stress tolerance, and early vigor, plants comprising the polynucleotides, polypeptides, and expression constructs, and methods of producing transgenic plants.