The present invention relates to isolated nucleic acid molecules and their corresponding encoded polypeptides able to confer the traits of improved nitrogen use efficiency 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 improved nitrogen use efficiency that leads to improvement in plant size, vegetative growth, growth rate, seedling vigor and/or biomass that are altered with respect to wild type plants grown under normal and/or abnormal nitrogen conditions.