Linking glucose signaling to nitrogen utilization by the OsHXK7-ARE4 complex in rice.

How reciprocal regulation of carbon and nitrogen metabolism works is a long-standing question. In plants, glucose and nitrate are proposed to act as signaling molecules, regulating carbon and nitrogen metabolism via largely unknown mechanisms. Here, we show that the MYB-related transcription factor ARE4 coordinates glucose signaling and nitrogen utilization in rice. ARE4 is retained in the cytosol in complexing with the glucose sensor OsHXK7. Upon sensing a glucose signal, ARE4 is released, is translocated into the nucleus, and activates the expression of a subset of high-affinity nitrate transporter genes, thereby boosting nitrate uptake and accumulation. This regulatory scheme displays a diurnal pattern in response to circadian changes of soluble sugars. The are4 mutations compromise in nitrate utilization and plant growth, whereas overexpression of ARE4 increases grain size. We propose that the OsHXK7-ARE4 complex links glucose to the transcriptional regulation of nitrogen utilization, thereby coordinating carbon and nitrogen metabolism.

Transnitrosylation Mediated by the Non-canonical Catalase ROG1 Regulates Nitric Oxide Signaling in Plants.

The redox-based protein S-nitrosylation is a conserved mechanism modulating nitric oxide (NO) signaling and has been considered mainly as a non-enzymatic reaction. S-nitrosylation is regulated by the intracellular NO level that is tightly controlled by S-nitrosoglutathione reductase (GSNOR). However, the molecular mechanisms regulating S-nitrosylation selectivity remain elusive. Here, we characterize an Arabidopsis "repressor of" gsnor1 (rog1) mutation that specifically suppresses the gsnor1 mutant phenotype. ROG1, identical to the non-canonical catalase, CAT3, is a transnitrosylase that specifically modifies GSNOR1 at Cys-10. The transnitrosylase activity of ROG1 is regulated by a unique and highly conserved Cys-343 residue. A ROG1C343T mutant displays increased catalase but decreased transnitrosylase activities. Consistent with these results, the rog1 mutation compromises responses to NO under both normal and stress conditions. We propose that ROG1 functions as a transnitrosylase to regulate the NO-based redox signaling in plants.