The autophagy receptor NBR1 directs the clearance of photodamaged chloroplasts.
The autophagy receptor NBR1 directs the clearance of photodamaged chloroplasts.
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DOI：
10.7554/elife.86030
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发表时间：
2023-04-18
期刊：
影响因子：
7.7
通讯作者：
Otegui MS
中科院分区：
文献类型：
--
作者：
Lee HN;Chacko JV;Gonzalez Solís A;Chen KE;Barros JAS;Signorelli S;Millar AH;Vierstra RD;Eliceiri KW;Otegui MS
与泛素结合的NBR1自噬受体在识别泛素化蛋白聚集体通过大范围自噬降解空泡方面发挥着重要作用。在这里，我们证明了当将拟南芥植物暴露在强光下时，NBR1独立于ATG7与光损伤的叶绿体相关联，ATG7是典型的自噬机制的核心组件。NBR1覆盖叶绿体的表面和内部，随后细胞器通过微自噬类型的过程直接吞噬到中央液泡中。NBR1在叶绿体中的重新定位不需要叶绿体转位蛋白复合体嵌入被膜中，而是通过去除NBR1的自我寡聚mPB1结构域而大大增强。NBR1修饰的叶绿体向液泡的转运依赖于NBR1泛素结合的UBA2结构域，但不依赖于泛素E3连接酶SP1和PUB4，后者是已知的指导叶绿体表面蛋白泛素化的酶。与野生型植物相比，nbr1突变体改变了一部分叶绿体蛋白的水平，并在高光照射下显示出异常的叶绿体密度和大小。我们推测，随着光损伤的叶绿体失去被膜的完整性，胞质连接酶到达叶绿体内部泛素化类囊体蛋白和基质蛋白，然后被NBR1识别以进行自噬清除。这项研究揭示了NBR1在微自噬降解受损叶绿体中的一个新功能。
The ubiquitin-binding NBR1 autophagy receptor plays a prominent role in recognizing ubiquitylated protein aggregates for vacuolar degradation by macroautophagy. Here, we show that upon exposing Arabidopsis plants to intense light, NBR1 associates with photodamaged chloroplasts independently of ATG7, a core component of the canonical autophagy machinery. NBR1 coats both the surface and interior of chloroplasts, which is then followed by direct engulfment of the organelles into the central vacuole via a microautophagy-type process. The relocalization of NBR1 into chloroplasts does not require the chloroplast translocon complexes embedded in the envelope but is instead greatly enhanced by removing the self-oligomerization mPB1 domain of NBR1. The delivery of NBR1-decorated chloroplasts into vacuoles depends on the ubiquitin-binding UBA2 domain of NBR1 but is independent of the ubiquitin E3 ligases SP1 and PUB4, known to direct the ubiquitylation of chloroplast surface proteins. Compared to wild-type plants, nbr1 mutants have altered levels of a subset of chloroplast proteins and display abnormal chloroplast density and sizes upon high light exposure. We postulate that, as photodamaged chloroplasts lose envelope integrity, cytosolic ligases reach the chloroplast interior to ubiquitylate thylakoid and stroma proteins which are then recognized by NBR1 for autophagic clearance. This study uncovers a new function of NBR1 in the degradation of damaged chloroplasts by microautophagy.