The phytohormone cytokinin influences many aspects of plant growth and development, several of which also involve the cellular process of autophagy, including leaf senescence, nutrient remobilization, and developmental transitions. The Arabidopsis type-A response regulators (type-A ARR) are negative regulators of cytokinin signaling that are transcriptionally induced in response to cytokinin. Here, we describe a mechanistic link between cytokinin signaling and autophagy, demonstrating that plants modulate cytokinin sensitivity through autophagic regulation of type-A ARR proteins. Type-A ARR proteins were degraded by autophagy in an AUTOPHAGY-RELATED (ATG)5-dependent manner, and this degradation is promoted by phosphorylation on a conserved aspartate in the receiver domain of the type-A ARRs. EXO70D family members interacted with type-A ARR proteins, likely in a phosphorylation-dependent manner, and recruited them to autophagosomes via interaction of the EXO70D AIM with the core autophagy protein, ATG8. Consistently, loss-of-function exo70D1,2,3 mutants exhibited compromised targeting of type-A ARRs to autophagic vesicles, have elevated levels of type-A ARR proteins, and are hyposensitive to cytokinin. Disruption of both type-A ARRs and EXO70D1,2,3 compromised survival in carbon-deficient conditions, suggesting interaction between autophagy and cytokinin responsiveness in response to stress. These results indicate that the EXO70D proteins act as selective autophagy receptors to target type-A ARR cargos for autophagic degradation, demonstrating modulation of cytokinin signaling by selective autophagy.

植物激素细胞分裂素影响植物生长和发育的许多方面，其中一些还涉及自噬的细胞过程，包括叶片衰老，养分迁移和发育过渡。在拟南芥A型应答调节剂（A ARR型）是细胞分裂素信号转导的负调节剂，响应细胞分裂素被转录诱导。在这里，我们描述了细胞分裂素信号传导和自噬之间的机制联系，表明植物通过A型ARR蛋白的自噬调节来调节细胞分裂素的敏感性。A型ARR蛋白通过自噬以自噬相关（ATG）5依赖的方式降解，并且该降解通过A型ARR受体结构域中保守的天冬氨酸上的磷酸化促进。EXO70D家族成员可能以磷酸化依赖性方式与A型ARR蛋白相互作用，并通过EXO70D AIM与核心自噬蛋白ATG8的相互作用将其募集到自噬体中。一致地，功能丧失exo70D1,2,3突变体表现出A型ARR靶向自噬囊泡的功能受损，A型ARR蛋白水平升高以及对细胞分裂素敏感性低下。A型两者的破坏ARRS和EXO70D1,2,3在碳缺少条件损害存活，表明响应于应力自噬和细胞分裂素响应之间的相互作用。这些结果表明，EXO70D蛋白充当靶向A型ARR货物自噬降解的选择性自噬受体，证明了选择性自噬对细胞分裂素信号传导的调节。