A positive feedback regulation of SnRK1 signaling by autophagy in plants

SnRK1,an evolutionarily conserved heterotrimeric kinase complex that acts as a key metabolic sensor in maintaining energy homeostasis in plants,is an important upstream activator of autophagy that serves as a cellular degradation mechanism for the healthy growth of plants.However,whether and how the autophagy pathway is involved in regulating SnRK1 activity remains unknown.In this study,we identified a clade of plant-specific and mitochondria-localized Fcs-like zinc finger(FLZ)proteins as currently unknown ATG8-interacting partners that actively inhibit SnRK1 signaling by repressing the T-loop phosphorylation of the catalyticαsubunits of SnRK1,thereby negatively modulating autophagy and plant tolerance to energy deprivation caused by long-term carbon starvation.Interestingly,these AtFLZs are transcriptionally repressed by low-energy stress,and AtFLZ proteins undergo a selective autophagy-dependent pathway to be delivered to the vacuole for degradation,thereby constituting a positive feedback regulation to relieve their repression of SnRK1 signaling.Bioinformatic analyses show that the ATG8-FLZ-SnRK1 regulatory axis first appears in gymnosperms and seems to be highly conserved during the evolution of seed plants.Consistent with this,depletion of ATG8-interacting ZmFLZ14 confers enhanced tolerance,whereas overexpression of ZmFLZ14 leads to reduced tolerance to energy deprivation in maize.Collectively,our study reveals a previously unknown mechanism by which autophagy contributes to the positive feedback regulation of SnRK1 signaling,thereby enabling plants to better adapt to stressful environments.

Amino Acid Catabolism in Plants

Amino acids have various prominent functions in plants. Besides their usage during protein biosynthesis, they also represent building blocks for several other biosynthesis pathways and play pivotal roles during signaling processes as well as in plant stress response. In general, pool sizes of the 20 amino acids differ strongly and change dynamically depending on the developmental and physiological state of the plant cell. Besides amino acid biosynthesis, which has already been investigated in great detail, the catabolism of amino acids is of central importance for adjusting their pool sizes but so far has drawn much less attention. The degradation of amino acids can also contribute substantially to the energy state of plant cells under certain physiological conditions, e.g. carbon starvation. In this review, we discuss the biological role of amino acid catabolism and summarize current knowledge on amino acid degradation pathways and their regulation in the context of plant cell physiology.

The plant circadian clock regulates autophagy rhythm through transcription factor LUX ARRHYTHMO

Autophagy is an evolutionarily conserved degradation pathway in eukaryotes;it plays a critical role in nutritional stress tolerance.The circadian clock is an endogenous timekeeping system that generates biological rhythms to adapt to daily changes in the environment.Accumulating evidence indicates that the circadian clock and autophagy are intimately interwoven in animals.However,the role of the circadian clock in regulating autophagy has been poorly elucidated in plants.Here,we show that autophagy exhibits a robust circadian rhythm in both light/dark cycle(LD)and in constant light(LL)in Arabidopsis.However,autophagy rhythm showed a different pattem with a phase-advance shift and a lower amplitude in LL compared to LD.Moreover,mutation of the transcription factor LUX ARRHYTHMO(LUX)removed autophagy rhythm in LL and led to an enhanced amplitude in LD.LUX represses expression of the core autophagy genes ATG2,ATG8 a,and ATG11 by directly binding to their promoters.Phenotypic analysis revealed that LUX is responsible for improved resistance of plants to carbon starvation,which is dependent on moderate autophagy activity.Comprehensive transcriptomic analysis revealed that the autophagy rhythm is ubiquitous in plants.Taken together,our findings demonstrate that the LUXmediated circadian clock regulates plant autophagy rhythms.