An appropriate concentration of arginine is required for normal root growth in rice.

Plant roots play an important role in uptake of water and nutrients, support of above-ground part and environmental sensing, but the molecular mechanisms underlying the root development are poorly understood in rice. We found that a gene (OsASL1) encoding argininosuccinate lyase is involved in normal root development of rice. OsASL1 cleaves argininosuccinate to arginine and fumarate reversibly, the last step in the arginine biosynthetic pathway. Here, we further characterized OsASL1 in terms of expression pattern, subcellular localization, and arginine effect on the root growth. A detailed expression analysis revealed that 2 transcripts of OsASL1, OsASL1.1 and OsASL1.2, showed different expression patterns; OsASL1.1 was expressed in most organs throughout the whole growth period, whereas OsASL1.2 was mainly expressed in the roots. In contrast to plastid-localized OsASL1.1, OsASL1.2 was localized to the cytosol and nucleus. The short-root phenotype of the mutant was not rescued by exogenous addition of the sodium nitroprusside, a nitric oxide donor, but rescued by an appropriate concentration of Arg. Our results indicate that the subcellular localization was determined by the N terminus of OsASL1 and that appropriate concentration of Arg is required for normal root elongation in rice.