Type One Protein Phosphatase Regulates Fixed-Carbon Starvation-Induced 1 Autophagy by Dephosphorylating ATG 13 a to Facilitate ATG 1 a-ATG 13 a 2 Formation in Arabidopsis 3

14 Autophagy, a conserved pathway which carries out the bulk degradation of 15 cytoplasmic material in eukaryotic cells, is critical in plant physiology and 16 development. It is tightly regulated by ATG13, a core component of ATG1 kinase 17 complex which initiates autophagy. Although it has been reported that ATG13 is 18 dephosphorylated immediately after nutrient starvation, the phosphatase regulating 19 this process is poorly understood. Here, we demonstrated that the septuple mutant 20 (topp-7m) and octuple mutant (topp-8m) of type one protein phosphatase (TOPP) 21 exhibited significantly reduced tolerance to fixed-carbon (C) starvation due to 22 compromised autophagy activity. Genetic analysis placed TOPP upstream of 23 autophagy. Interestingly, ATG13a was found to be an interactor of TOPP. And TOPP 24 directly dephosphorylated ATG13a in vitro and in vivo. Meanwhile, eighteen 25 phosphorylation sites of ATG13a were identified by LC-MS. Mimic 26 was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which this version posted April 10, 2022. ; https://doi.org/10.1101/2022.04.10.487768 doi: bioRxiv preprint