Autophagy, a conserved pathway that carries out the bulk degradation of cytoplasmic material in eukaryotic cells, is critical for plant physiology and development. This process is tightly regulated by ATG13, a core component of the ATG1 kinase complex, which initiates autophagy. Although ATG13 is known to be dephosphorylated immediately after nutrient starvation, the phosphatase regulating this process is poorly understood. Here, we determined that the Arabidopsis (Arabidopsis thaliana) septuple mutant (topp-7m) and octuple mutant (topp-8m) of TYPE ONE PROTEIN PHOSPHATASE (TOPP) exhibited significantly reduced tolerance to fixed-carbon (C) starvation due to compromised autophagy activity. Genetic analysis placed TOPP upstream of autophagy. Interestingly, ATG13a was found to be an interactor of TOPP. TOPP directly dephosphorylated ATG13a in vitro and in vivo. We identified 18 phosphorylation sites in ATG13a by LC-MS. Phospho-dead ATG13a at these 18 sites significantly promoted autophagy and increased the tolerance of the atg13ab mutant to fixed-C starvation. The dephosphorylation of ATG13a facilitated ATG1a-ATG13a complex formation. Consistently, the recruitment of ATG13a for ATG1a was markedly inhibited in topp-7m-1. Finally, TOPP-controlled dephosphorylation of ATG13a boosted ATG1a phosphorylation. Taken together, our study reveals the crucial role of TOPP in regulating autophagy by stimulating the formation of the ATG1a-ATG13a complex by dephosphorylating ATG13a in Arabidopsis.

中文翻译：

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一型蛋白磷酸酶调节拟南芥中固定碳饥饿诱导的自噬。

自噬是一种保守的途径，在真核细胞中进行细胞质物质的大量降解，对于植物生理学和发育至关重要。这一过程受到 ATG13 的严格调控，ATG13 是 ATG1 激酶复合物的核心成分，可启动自噬。尽管已知 ATG13 在营养饥饿后立即去磷酸化，但对调节这一过程的磷酸酶知之甚少。在这里，我们确定拟南芥（Arabidopsis thaliana）一型蛋白磷酸酶（TOPP）的七重突变体（topp-7m）和八重突变体（topp-8m）由于自噬受损而表现出对固定碳（C）饥饿的耐受性显着降低活动。遗传分析将 TOPP 置于自噬的上游。有趣的是，ATG13a被发现是TOPP的相互作用子。TOPP 在体外和体内直接去磷酸化 ATG13a。我们通过 LC-MS 鉴定了 ATG13a 中的 18 个磷酸化位点。这 18 个位点的磷酸化死亡 ATG13a 显着促进自噬并增加 atg13ab 突变体对固定 C 饥饿的耐受性。ATG13a 的去磷酸化促进了 ATG1a-ATG13a 复合物的形成。一致的是，在 topp-7m-1 中 ATG13a 募集 ATG1a 受到显着抑制。最后，TOPP 控制的 ATG13a 去磷酸化增强了 ATG1a 磷酸化。综上所述，我们的研究揭示了拟南芥中 TOPP 通过使 ATG13a 去磷酸化来刺激 ATG1a-ATG13a 复合物的形成，从而在调节自噬中发挥关键作用。