Evolution of Two Ubiquitin-like System of Autophagy in Orchid

As an important horticultural plant, the orchid is widely distributed in its natural habitat and faces various environmental stresses, among which nutrient recycling and stress resistance are of great concern. During these processes, autophagy is an essential pathway, which is a conserved self-eating process that degrades macromolecular components and recycles cell materials or nutrients during developmental processes or under stress conditions. Two ubiquitin-like systems (UBLs) play a major role in the initiation of autophagy and are associated with two key proteins: ATG8 and ATG12. In this study, we identified and refined the UBL-related genes in orchids and performed phylogenetic reconstruction together with other plant species. We found that the orchid had unique domains in UBL-related genes, indicating potential functional diversification in the ATG8 system in plants. Transcriptome and protein tertiary structure prediction indicated that conserved domains that are vital for the canonical function of ATG12 are incomplete in orchids, in which a novel mechanism of autophagy may have evolved.