Jain Vanita, Kaiser Werner, Huber Steven C
Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 USA.
Plant Cell Physiol. 2008 May;49(5):843-52. doi: 10.1093/pcp/pcn060. Epub 2008 Apr 16.
Under normal conditions, plants contain numerous carbonylated proteins, which are thought to be indicative of oxidative stress damage. Conditions that promote formation of reactive oxygen species (ROS) enhance protein carbonylation, and protein degradation is required to reverse the damage. However, it is not clear how the degradation of carbonylated proteins is controlled in planta. In this report, we show that detached Arabidopsis leaves rapidly and selectively degrade carbonylated proteins when kept in the dark. The loss of carbonylated proteins corresponded to a loss of soluble protein and accumulation of free amino acids. Degradation of carbonylated proteins and the loss of soluble protein was blocked by MG132 but not 3-methyladenine, suggesting that the 26S proteasome pathway rather than the autophagic pathway was involved. Consistent with this, rpn10 and rpn12 mutants, which are defective in proteasome function, had increased (rather than decreased) levels of carbonylated proteins when detached in the dark. Feeding metabolites (amino acids and sucrose) to detached leaves of wild-type Arabidopsis in the dark had little or no effect on the loss of carbonylated proteins, whereas providing soybean xylem sap via the transpiration stream effectively prevented degradation. The effect of xylem sap was mimicked by feeding 10 muM kinetin. We postulate that disruption of cytokinin flux to detached leaves triggers the selective degradation of carbonylated proteins via the proteasome pathway. The results may have implications for the control of protein mobilization in response to changes in N availability.
在正常条件下，植物含有大量羰基化蛋白质，这些蛋白质被认为是氧化应激损伤的指示物。促进活性氧（ROS）形成的条件会增强蛋白质羰基化，并且需要蛋白质降解来逆转这种损伤。然而，尚不清楚在植物中羰基化蛋白质的降解是如何被控制的。在本报告中，我们表明离体的拟南芥叶片在黑暗中时会快速且选择性地降解羰基化蛋白质。羰基化蛋白质的损失与可溶性蛋白质的损失以及游离氨基酸的积累相对应。羰基化蛋白质的降解和可溶性蛋白质的损失被MG132阻断，但未被3 - 甲基腺嘌呤阻断，这表明涉及的是26S蛋白酶体途径而非自噬途径。与此一致的是，蛋白酶体功能有缺陷的rpn10和rpn12突变体在黑暗中离体时羰基化蛋白质水平升高（而非降低）。在黑暗中向野生型拟南芥的离体叶片投喂代谢物（氨基酸和蔗糖）对羰基化蛋白质的损失几乎没有影响，而通过蒸腾流提供大豆木质部汁液可有效防止降解。用10 μM激动素投喂可模拟木质部汁液的作用。我们推测细胞分裂素向离体叶片的通量中断会触发通过蛋白酶体途径对羰基化蛋白质的选择性降解。这些结果可能对响应氮素有效性变化时蛋白质动员的控制具有启示意义。
