Autophagy is essential for somatic embryogenesis in citrus through regulating amyloplast degradation and lipid homeostasis

Autophagy is a conserved degradation pathway that regulates the clearance of paternal substrate at the early embryogenesis stage of animals. However, its mode of action is likely different in plants, which can regenerate through apomixis without fertilisation. Somatic embryogenesis (SE) is a unique plant process widely used for plant propagation and germplasm utilisation. Here, we studied citrus as an example and found a higher autophagic activity after SE initiation. Interestingly, amyloplasts were frequently found inside autophagosomes, whereas the inhibition of autophagy blocks amyloplasts/starch degradation and hinders somatic embryo formation. Furthermore, the consumption of storage lipids was faster in autophagy mutants, suggesting lipid metabolism is activated when starch utilisation is blocked. Exogenous application of autophagy-inducing chemicals (e.g. spermidine) significantly promoted the formation of autophagosomes and increased SE efficiency, indicating a positive correlation between autophagy, energy metabolism, and somatic embryo formation in citrus. Taken together, our study unveils a pathway for the degradation of plant-specific organelles and provides an effective approach for plant propagation.