Soto-Burgos Junmarie, Bassham Diane C
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa, United States of America.
Plant Sciences Institute, Iowa State University, Ames, Iowa, United States of America.
PLoS One. 2017 Aug 4;12(8):e0182591. doi: 10.1371/journal.pone.0182591. eCollection 2017.
Autophagy is a degradation process in which cells break down and recycle their cytoplasmic contents when subjected to environmental stress or during cellular remodeling. The Arabidopsis thaliana SnRK1 complex is a protein kinase that senses changes in energy levels and triggers downstream responses to enable survival. Its mammalian ortholog, AMPK, and yeast ortholog, Snf-1, activate autophagy in response to low energy conditions. We therefore hypothesized that SnRK1 may play a role in the regulation of autophagy in response to nutrient or energy deficiency in Arabidopsis. To test this hypothesis, we determined the effect of overexpression or knockout of the SnRK1 catalytic subunit KIN10 on autophagy activation by abiotic stresses, including nutrient deficiency, salt, osmotic, oxidative, and ER stress. While wild-type plants had low basal autophagy activity in control conditions, KIN10 overexpression lines had increased autophagy under these conditions, indicating activation of autophagy by SnRK1. A kin10 mutant had a basal level of autophagy under control conditions similar to wild-type plants, but activation of autophagy by most abiotic stresses was blocked, indicating that SnRK1 is required for autophagy induction by a wide variety of stress conditions. In mammals, TOR is a negative regulator of autophagy, and AMPK acts to activate autophagy both upstream of TOR, by inhibiting its activity, and in a parallel pathway. Inhibition of Arabidopsis TOR leads to activation of autophagy; inhibition of SnRK1 did not block this activation. Furthermore, an increase in SnRK1 activity was unable to induce autophagy when TOR was also activated. These results demonstrate that SnRK1 acts upstream of TOR in the activation of autophagy in Arabidopsis.
自噬是一种降解过程，在该过程中，细胞在受到环境压力或细胞重塑期间会分解并循环利用其细胞质内容物。拟南芥SnRK1复合体是一种蛋白激酶，可感知能量水平的变化并触发下游反应以确保生存。其在哺乳动物中的直系同源物AMPK以及在酵母中的直系同源物Snf-1，会在低能量条件下激活自噬。因此，我们推测SnRK1可能在拟南芥对营养或能量缺乏的自噬调节中发挥作用。为了验证这一假设，我们确定了SnRK1催化亚基KIN10的过表达或敲除对包括营养缺乏、盐、渗透、氧化和内质网应激在内的非生物胁迫激活自噬的影响。在对照条件下，野生型植物的基础自噬活性较低，而KIN10过表达株系在这些条件下自噬增加，表明SnRK1激活了自噬。kin10突变体在对照条件下的自噬基础水平与野生型植物相似，但大多数非生物胁迫对自噬的激活被阻断，这表明SnRK1是多种胁迫条件下自噬诱导所必需的。在哺乳动物中，TOR是自噬的负调节因子，AMPK通过抑制TOR的活性在TOR上游以及在平行途径中发挥作用来激活自噬。抑制拟南芥TOR会导致自噬激活；抑制SnRK1并未阻断这种激活。此外，当TOR也被激活时，SnRK1活性的增加无法诱导自噬。这些结果表明，在拟南芥自噬激活过程中，SnRK1在TOR上游发挥作用。
