Li Faqiang, Chung Taijoon, Pennington Janice G, Federico Maria L, Kaeppler Heidi F, Kaeppler Shawn M, Otegui Marisa S, Vierstra Richard D
Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706.
Department of Botany, University of Wisconsin, Madison, Wisconsin 53706.
Plant Cell. 2015 May;27(5):1389-408. doi: 10.1105/tpc.15.00158. Epub 2015 May 5.
Autophagy is a primary route for nutrient recycling in plants by which superfluous or damaged cytoplasmic material and organelles are encapsulated and delivered to the vacuole for breakdown. Central to autophagy is a conjugation pathway that attaches AUTOPHAGY-RELATED8 (ATG8) to phosphatidylethanolamine, which then coats emerging autophagic membranes and helps with cargo recruitment, vesicle enclosure, and subsequent vesicle docking with the tonoplast. A key component in ATG8 function is ATG12, which promotes lipidation upon its attachment to ATG5. Here, we fully defined the maize (Zea mays) ATG system transcriptionally and characterized it genetically through atg12 mutants that block ATG8 modification. atg12 plants have compromised autophagic transport as determined by localization of a YFP-ATG8 reporter and its vacuolar cleavage during nitrogen or fixed-carbon starvation. Phenotypic analyses showed that atg12 plants are phenotypically normal and fertile when grown under nutrient-rich conditions. However, when nitrogen-starved, seedling growth is severely arrested, and as the plants mature, they show enhanced leaf senescence and stunted ear development. Nitrogen partitioning studies revealed that remobilization is impaired in atg12 plants, which significantly decreases seed yield and nitrogen-harvest index. Together, our studies demonstrate that autophagy, while nonessential, becomes critical during nitrogen stress and severely impacts maize productivity under suboptimal field conditions.
自噬是植物中营养物质循环利用的主要途径，通过该途径，多余或受损的细胞质物质和细胞器被包裹起来并输送到液泡中进行分解。自噬的核心是一种缀合途径，该途径将自噬相关蛋白8（ATG8）与磷脂酰乙醇胺连接，然后磷脂酰乙醇胺包被新形成的自噬膜，并有助于货物招募、囊泡包裹以及随后囊泡与液泡膜的对接。ATG8功能的一个关键组分是ATG12，它在与ATG5结合后促进脂化作用。在这里，我们通过转录方式全面定义了玉米（Zea mays）的自噬系统，并通过阻断ATG8修饰的atg12突变体对其进行了遗传表征。通过YFP-ATG8报告基因的定位及其在氮或固定碳饥饿期间的液泡切割情况确定，atg12植株的自噬转运受损。表型分析表明，在营养丰富的条件下生长时，atg12植株的表型正常且可育。然而，在氮饥饿时，幼苗生长严重受阻，随着植株成熟，它们表现出叶片衰老加剧和穗发育不良。氮分配研究表明，atg12植株的氮素再利用受损，这显著降低了种子产量和氮收获指数。总之，我们的研究表明，自噬虽然不是必需的，但在氮胁迫期间变得至关重要，并在次优田间条件下严重影响玉米的生产力。
