About this Research Topic
Sugars perform important regulatory roles in a wide range of processes in plants. They use different signalling mechanisms, including HXK-mediated glucose sensing, the SNF1-related kinase 1 (SnRK1) and target of rapamycin (TOR) protein kinases. The TOR complex is a master regulator of cell growth and metabolism and is activated by glucose metabolism. TOR is negatively regulated by SnRK1, which acts as a metabolic sensor to control metabolism according to the cell’s energy status and requirements and is regulated by an array of sugar-phosphates, such as glucose-1-phosphate, glucose-6-phosphate and trehalose-6-phosphate.
Interestingly, autophagy - a process by which cellular components are recycled at basal levels during normal growth conditions, and at higher levels during (a)biotic stresses, nutritional deficiency or at certain developmental stages - has been shown to be inhibited by TOR and stimulated by SnRK1.
This links sugars and energy status to autophagy, especially during stress responses. From an energetic point of view, a lack of sugars can stimulate autophagy (starvation-induced) but undoubtedly positive sugar signals interact with TOR and autophagy signalling, embedded in a network of many other players that are involved in crosstalk with different hormone signalling pathways. However, these links remain poorly understood to date. In addition, ER stress-mediated autophagy seems to occur in a TOR-independent manner. Whether specific sugars play a role in this process remains unknown.
Autophagy is essential for plant adaptation to environmental changes. The role of sugars in the control of the molecular mechanisms underpinning autophagy remains mostly unexplored in plants and this deserves further attention. Through the availability of (i) a large collection of Arabidopsis thaliana mutants with altered autophagic activity; (ii) transgenic (reporter) lines that facilitate the study of autophagosome biogenesis and; (iii) mutants affected in sugar signalling pathways, we expect breakthroughs in this rapidly evolving research area in the near future. Once the underlying mechanisms become better understood, this opens the door to an array of unprecedented practical applications related to plant stress adaptation as well as plant development.
The objective of this Research Topic is to show the importance of sugars in plant autophagy, not only as a source of carbon and energy but also as signalling molecules. Therefore, Original Research Articles, Opinion, Perspectives and comprehensive Reviews are welcome for submission. In particular, we aim to collect evidence focused on:
• The types of sugars and sugar-derived signals affecting autophagy
• The effect of sugars on autophagosome formation and function
• The molecular mechanisms by which sugars regulate autophagy
• The relation between sugar and nitrogen starvation-induced autophagy
• The role of sugars in biotic and abiotic stress-induced autophagy
• The impact of sugars on oxidative stress-induced autophagy
The evidence presented within this Research Topic will contribute to our understanding of the molecular mechanisms by which sugars modulate plant autophagy and will open new questions and orient further research in the plant science field.
Keywords: ATG genes, Autophagy, Sugar Signalling, Senescence, Stress Response
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