The AMP-Activated Protein Kinase KIN10 Is Involved in the Regulation of Autophagy in Arabidopsis.

Liang Chen,Hua Qi,Fan-Nv Xia,Qin-Fang Chen,Li-Juan Xie,Ze-Zhuo Su,Li Huang,Shi Xiao

doi:10.3389/fpls.2017.01201

Abstract

Autophagy is a highly conserved system in eukaryotes for the bulk degradation and recycling of intracellular components. Autophagy is involved in many physiological processes including development, senescence, and responses to abiotic and biotic stress. The adenosine 5’-monophosphate (AMP)-activated protein kinase AMPK positively regulates autophagy in mammals; however, the potential function of AMPK in plant autophagy remains largely unknown. Here, we identified KIN10, a plant ortholog of the mammalian AMPK, as a positive regulator of plant autophagy and showed that it acts by affecting the phosphorylation of ATG1 (AUTOPHAGY-RELATED GENE 1) proteins in Arabidopsis. Transgenic Arabidopsis lines overexpressing KIN10 (KIN10-OE) showed delays in leaf senescence, and increased tolerance to nutrient starvation, these phenotypes required a functional autophagy pathway. Consistent with KIN10 having a potential role in autophagy, the nutrient starvation-induced formation of autophagosomes and cleavage of GFP-ATG8e were accelerated in the KIN10-OE lines compared to the wild type. Moreover, the KIN10-OE lines were less sensitive to drought and hypoxia treatments, compared with wild type. Carbon starvation enhanced the level of phosphorylated YFP-ATG1a in the KIN10-OE lines compared to that of wild type. Together, these findings suggest that KIN10 is involved in positive regulation of autophagy, possibly by affecting the phosphorylation of ATG1s in Arabidopsis.

Highlights

Autophagy is the process of degradation and recycling of cytoplasmic organelles, proteins, and macromolecules, and is highly conserved among eukaryotes
To examine the potential role of Arabidopsis KIN10 in autophagy, we further examined the response of the KIN10-OE lines and KIN10 RNA interference lines (RNAi-1 and RNAi-7) to naturally induced senescence and nutrient deficiency
The enhanced tolerance to starvation in the OE-1 line was further supported by the higher survival rates (Figure 2C) and higher relative chlorophyll contents (Figure 2D) in this line. These results indicate that the enhanced tolerance to nutrient starvation in the KIN10-OE lines is dependent on a functional autophagy pathway

Summary

Introduction

Autophagy is the process of degradation and recycling of cytoplasmic organelles, proteins, and macromolecules, and is highly conserved among eukaryotes. Autophagy is activated by a variety of stress factors, such as nutrient deprivation, hypoxia, reactive oxygen species, and infection by pathogen (Kroemer et al, 2010; Han et al, 2011). Autophagy plays an essential role in the maintenance of cellular homeostasis under changing nutrient conditions. Among the three types of autophagy, macroautophagy (hereafter referred to as autophagy) is the predominant form (Klionsky, 2007). Double-membrane vesicles, called autophagosomes, are formed from the expanding membranes of preautophagosomal structures; these autophagosomes sequester the enclosed components and deliver them to the lysosome/vacuole for degradation.

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