Cyanobacterial NOS expression improves nitrogen use efficiency, nitrogen-deficiency tolerance and yield in Arabidopsis

Developing strategies to improve nitrogen (N) use efficiency (NUE) in plants is a challenge to reduce environmental problems linked to over-fertilization. The nitric oxide synthase (NOS) enzyme from the cyanobacteria Synechococcus PCC 7335 (SyNOS) has been recently identified and characterized. SyNOS catalyzes the conversion of arginine to citrulline and nitric oxide (NO), and then 70% of the produced NO is rapidly oxidized to nitrate by an unusual globin domain in its 5'-terminus. In this study, we assessed whether SyNOS expression in plants affects N metabolism improving NUE and yield. Our results showed that transgenic Arabidopsis plants had higher primary shoot length and shoot branching when grown in N-deficient conditions and higher seed production in N-sufficient and -deficient conditions. Moreover, transgenic plants showed significantly increased NUE in both N conditions. No differences were observed in N uptake for SyNOS lines. However, SyNOS lines presented an increase in N assimilation/remobilization under low N conditions. In addition, SyNOS lines had greater N-deficiency tolerance compared to wt plants. Our results support that SyNOS expression generates a positive effect on N metabolism and seed production in Arabidopsis, and it might be envisaged as a strategy to improve productivity in crops under adverse N environments.