The present invention relates to isolated nucleic acid molecules and their corresponding encoded polypeptides able confer the trait of modulated plant size, vegetative growth, organ number, plant architecture, growth rate, seedling vigor and/or biomass in plants. The present invention further relates to the use of these nucleic acid molecules and polypeptides in making transgenic plants, plant cells, plant materials or seeds of a plant having plant size, vegetative growth, organ number, plant architecture, growth rate, seedling vigor and/or biomass that are altered with respect to wild type plants grown under similar conditions