Abstract
Autophagy is a catabolic and recycling pathway that maintains cellular homeostasis under normal growth and stress conditions. Two major types of autophagy, microautophagy and macroautophagy, have been described in plants. During macroautophagy, cellular content is engulfed by a double-membrane vesicle called autophagosome. This vesicle fuses its outer membrane with the tonoplast and releases the content into the vacuole for degradation. During certain developmental processes, autophagy is enhanced by induction of several autophagy-related genes (ATG genes). Autophagy in crop development has been studied in relation to leaf senescence, seed and reproductive development, and vascular formation. However, its role in fruit ripening has only been partially addressed. Strawberry is an important berry crop, representative of non-climacteric fruit. We have analyzed the occurrence of autophagy in developing and ripening fruits of the cultivated strawberry. Our data show that most ATG genes are conserved in the genome of the cultivated strawberry Fragaria x ananassa and they are differentially expressed along the ripening of the fruit receptacle. ATG8-lipidation analysis proves the presence of two autophagic waves during ripening. In addition, we have confirmed the presence of autophagy at the cellular level by the identification of autophagy-related structures at different stages of the strawberry ripening. Finally, we show that blocking autophagy either biochemically or genetically dramatically affects strawberry growth and ripening. Our data support that autophagy is an active and essential process with different implications during strawberry fruit ripening.
Highlights
Autophagy is a general mechanism in eukaryotes that maintains the cell homeostasis through the degradation of intracellular targeted organelles, proteins, and major compounds (Marshall and Vierstra, 2018)
It is interesting to note that the number of genes belonging to each family in the diploid F. vesca was very similar to Arabidopsis thaliana, including those described as single copy genes
Our study shows that strawberry receptacle is a place of constant autophagy activity with two points of autophagy flux induction
Summary
Autophagy is a general mechanism in eukaryotes that maintains the cell homeostasis through the degradation of intracellular targeted organelles, proteins, and major compounds (Marshall and Vierstra, 2018). Several autophagic routes have been described in animals, fungi, and plants, with the best known initially referred to as macroautophagy (hereafter named as autophagy) (Galluzzi et al, 2017) In this pathway, a double membrane structure is initiated that grows until its complete closure, engulfing cytoplasmic material and giving rise to a structure called autophagosome. Autophagy is driven by a set of core autophagy-related proteins (ATG) first described in yeast and conserved in almost all eukaryotes (Tsukada and Ohsumi, 1993; Meijer et al, 2007) They participate in all the stages of the pathway, from cargo recognition and autophagosome formation to docking to the vacuole and release of the content (Marshall and Vierstra, 2018)
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