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

Otto Teixeira Fraga,Iana Pedro Silva Quadros,Elizabeth Pacheco Batista Fontes,Bruno Paes De Melo,Pedro Augusto Braga Reis

doi:10.3390/ijms22158287

Abstract

Leaf senescence is a genetically regulated developmental process that can be triggered by a variety of internal and external signals, including hormones and environmental stimuli. Among the senescence-associated genes controlling leaf senescence, the transcriptional factors (TFs) comprise a functional class that is highly active at the onset and during the progression of leaf senescence. The plant-specific NAC (NAM, ATAF, and CUC) TFs are essential for controlling leaf senescence. Several members of Arabidopsis AtNAC-SAGs are well characterized as players in elucidated regulatory networks. However, only a few soybean members of this class display well-known functions; knowledge about their regulatory circuits is still rudimentary. Here, we describe the expression profile of soybean GmNAC-SAGs upregulated by natural senescence and their functional correlation with putative AtNAC-SAGs orthologs. The mechanisms and the regulatory gene networks underlying GmNAC081- and GmNAC030-positive regulation in leaf senescence are discussed. Furthermore, new insights into the role of GmNAC065 as a negative senescence regulator are presented, demonstrating extraordinary functional conservation with the Arabidopsis counterpart. Finally, we describe a regulatory circuit which integrates a stress-induced cell death program with developmental leaf senescence via the NRP-NAC-VPE signaling module.

Highlights

Leaf senescence is a developmentally programmed or environmentally induced process by which cells activate the programmed cell death response (PCD), resulting in the relocation of nutrients towards different organs
GmNAC085 is not considered a conceptual SAG, as it is downregulated during senescence, these findings strongly suggest that it may be associated with the control of environmental programmed cell death (ePCD) in soybean
The high conservation among NACs from different crops and plant model systems suggests that biological information regarding Arabidopsis NAC-SAGs may be transferable to the studies of crops

Summary

Introduction

Leaf senescence is a developmentally programmed or environmentally induced process by which cells activate the programmed cell death response (PCD), resulting in the relocation of nutrients towards different organs. The dismantling of chloroplasts generates the first visible indication of leaf senescence, leaf yellowing During this process, carbon assimilation is succeeded by the catabolism of chlorophyll, proteins, and lipids; thereby, their metabolized products are relocated to different organs [1,2]. The chloroplast dismantling steps do not occur simultaneously, as chlorophyll catabolism precedes protein degradation and structural changes [1] This entire process is tightly regulated by gene expression control and hormone signaling. The NAC transcription factors modulate several cell signaling responses and play significant roles in developmental, hormonal, and stress events [5,18,19,20,21]. We highlight the profiles of the senescence-associated GmNAC genes under different stress conditions and their possible connections with the leaf senescence process

Leaf Senescence-Associated GmNAC Genes

GmNAC-SAGs as Positive and Negative Regulators of Leaf Senescence

A Regulatory Circuit Integrating Stress-Induced with Natural Leaf Senescence

Findings

Conclusions