Melatonin activates the OsbZIP79–OsABI5 module that orchestrates nitrogen and ROS homeostasis to alleviate nitrogen-limitation stress in rice

Melatonin(Mel)has previously been reported to effectively alleviate nitrogen-limitation(N-L)stress and thus increase nitrogen-use efficiency(NUE)in several plants,but the underlying mechanism remains obscure.Here,we revealed that OsbZIP79(BASIC LEUCINE ZIPPER 79)is transcriptionally activated under N-L conditions,and its expression is further enhanced by exogenous Mel.By the combined use of omics,genetics,and biological techniques,we revealed that the OsbZIP79–OsABI5(ABSCISIC ACID INSENSITIVE 5)module stimulated regulation of reactive oxygen species(ROS)homeostasis and the uptake and metabolismof nitrogen under conditions of indoor nitrogen limitation(1/16 normal level).OsbZIP79 activated the transcription of OsABI5,and OsABI5 then bound to the promoters of target genes,including genes involved in ROS homeostasis and nitrogen metabolism,activating their transcription.This module was also indispensable for upregulation of several other genes involved in abscisic acid catabolism,nitrogen uptake,and assimilation under N-L and Mel treatment,although these genes were not directly transactivated by OsABI5.Field experiments demonstrated that Mel significantly improved rice growth under low nitrogen(L-N,half the normal level)by the same mechanism revealed in the nitrogen-limitation study.Mel application produced a 28.6%yield increase under L-N and thus similar increases in NUE.Also,two OsbZIP79-overexpression lines grown in L-N field plots had significantly higher NUE(+13.7%and+21.2%)than their wild types.Together,our data show that an OsbZIP79–OsABI5 module regulates the rice response to N insufficiency(N limitation or low N),which is important for increasing NUE in rice production.

Mitochondrial Composition,Function and Stress Response in Plants

The primary function of mitochondria is respiration, where catabolism of substrates is coupled to ATP synthesis via oxidative phosphorylation. In plants, mitochondrial composition is relatively complex and flexible and has specific pathways to support photosynthetic processes in illuminated leaves.

SPINDLY, ERECTA, and Its Ligand STOMAGEN Have a Role in Redox-Mediated Cortex Proliferation in the Arabidopsis Root

Reactive oxygen species （ROS） are harmful to all living organisms and therefore they must be removed to ensure normal growth and development. ROS are also signaling molecules, but so far little is known about the mecha- nisms of ROS perception and developmental response in plants. We here report that hydrogen peroxide induces cortex proliferation in the Arabidopsis root and that SPINDLY （SPY）, an O-linked glucosamine acetyltransferase, regulates cortex proliferation by maintaining cellular redox homeostasis. We also found that mutation in the leucine-rich receptor kinase ERECTA and its putative peptide ligand STOMAGEN block the effect of hydrogen peroxide on root cortex proliferation. However, ERECTA and STOMAGEN are expressed in the vascular tissue, whereas extra cortex cells are produced from the endodermis, suggesting the involvement of intercellular signaling~ SPY appears to act downstream of ERECTA, because the spy mutation still caused cortex proliferation in the erecta mutant background. We therefore have not only gained insight into the mechanism by which SPY regulates root development but also uncovered a novel pathway for ROS signal- ing in plants. The importance of redox-mediated cortex proliferation as a protective mechanism against oxidative stress is also discussed.