A Regulatory Circuit Integrating Stress-Induced with Natural Leaf Senescence

Abstract

Any condition that disrupts the ER homeostasis activates a cytoprotective signaling cascade, designated as the unfolded protein response (UPR), which is transduced in plant cells by a bipartite signaling module. Activation of IRE1/ bZIP60 and bZIP28/bZIP17, which represent the bipartite signaling arms and serve as ER stress sensors and transducers, results in the upregulation of ER protein processing machinery-related genes to recover from stress. However, if the ER stress persists and the cell is unable to restore ER homeostasis, programmed cell death signaling pathways are activated for survival. Here, we describe an ER stress-induced plant-specific cell death program, which is a shared response to multiple stress signals. This signaling pathway was first identified through genome-wide expression profile of differentially expressed genes in response to combined ER stress and osmotic stress. Among them, the development and cell death domain-containing N-rich proteins (DCD/NRPs), NRP-A and NRP-B, and the transcriptional factor GmNAC81 were selected as mediators of cell death in plants. These genes were used as targets to identify additional components of the cell death pathway, which is described here as a regulatory circuit that integrates a stress-induced cell death program with leaf senescence via the NRP-A/NRP-B/GmNAC81:GmNAC30/VPE signaling module.

Senescence-Associated Glycine max (Gm)NAC Genes: Integration of Natural and Stress-Induced Leaf Senescence

“…A consensus theme that has emerged from studies of regulatory networks controlling leaf senescence is the existence of a signaling module in plants integrating the transduction of environmental and developmental signals at the onset and progression of leaf senescence. In soybean, the developmental cell death (DCD) domain-containing asparagine-rich protein (NRP)-mediated cell death response has been characterized as a regulatory circuit that integrates stress-induced with developmentally programmed leaf senescence [ 57 , 116 ].…”

“…The DCD/NRP-mediated cell death signaling pathway, which has been uncovered in soybean, transduces a cell death signal derived from multiple stress conditions and late stages of leaf development [ 116 ]. The first components of this cell death pathway identified were DCD/NRPs, designated GmNRP-A and GmNRP-B, which gave the pathway its name (NRP signaling; Figure 2 ).…”