Nitric Oxide Is Required for Primary Nitrate Response in Arabidopsis: Evidence for S-Nitrosation of NLP7.

Nitrogen (N) is a necessary nutrient for plant development and seed production, with nitrate (NO) serving as the primary source of N in soils. Although several molecular players in plant responses to NO signaling were unraveled, it is still a complex process with gaps that require further investigation. The aim of our study is to analyze the role of nitric oxide (NO) in the primary nitrate response (PNR). Using a combination of genetic and pharmacological approaches, we demonstrate that NO is required for the expression of the NO-regulated genes nitrate reductase 1 (), nitrite reductase (), and nitrate transporters (nitrate transporter 1.1 [] and nitrate transporter 2.1 []) in Arabidopsis. The PNR is impaired in the Arabidopsis mutant , defective in NO production. Our results also show that (), involved in NO homeostasis, is rapidly induced during PNR in wild type (wt) but not in the mutants of the nitrate transceptor NTR1.1 and the transcription factor nodule inception-like protein 7 (NLP7), suggesting that the NRT1.1-NLP7 cascade modulates gene expression. Biotin switch experiments demonstrate that NLP7, the PNR-master regulator, is S-nitrosated . Depletion of NO during PNR intensifies the decrease in reactive oxygen species levels and the rise of catalase (CAT) and ascorbate peroxidase (APX) enzyme activity. NO, a by-product of NO metabolism and a well-characterized signal molecule in plants, is an important player in the PNR.