Sphingolipids act as regulators of programmed cell death (PCD) and the plant defence response. The homeostasis between long-chain base (LCB) and ceramide (Cer) seems to play an important role in executions of PCD. Therefore, deciphering the role of neutral ceramidases (NCER) is crucial to identify the sphingolipid compounds that trigger and execute PCD. We performed comprehensive sphingolipid and phytohormone analyses of Arabidopsis ncer mutants, combined with gene expression profiling and microscopic analyses. While ncer1 exhibited early leaf senescence (developmentally controlled PCD - dPCD) and an increase in hydroxyceramides, ncer2 showed spontaneous cell death (pathogen-triggered PCD-like - pPCD) accompanied by an increase in LCB t18:0 at 35 d, respectively. Loss of NCER1 function resulted in accumulation of jasmonoyl-isoleucine (JA-Ile) in the leaves, whereas disruption of NCER2 was accompanied by higher levels of salicylic acid (SA) and increased sensitivity to Fumonisin B1 (FB1 ). All mutants were also found to activate plant defence pathways. These data strongly suggest that NCER1 hydrolyses ceramides whereas NCER2 functions as a ceramide synthase. Our results reveal an important role of NCER in the regulation of both dPCD and pPCD via a tight connection between the phytohormone and sphingolipid levels in these two processes.

中文翻译：

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拟南芥中性ceramidases 1和2的中断导致特定的鞘脂失衡，触发不同的依赖植物激素的植物细胞死亡程序。

鞘脂充当程序性细胞死亡（PCD）和植物防御反应的调节剂。长链碱基（LCB）和神经酰胺（Cer）之间的体内平衡似乎在PCD的执行中起着重要作用。因此，破译中性ceramidases（NCER）的作用对于确定触发和执行PCD的鞘脂化合物至关重要。我们对拟南芥ncer突变体进行了鞘脂和植物激素的全面分析，并结合了基因表达谱和显微分析。虽然ncer1表现出早期叶片衰老（发育受控制的PCD-dPCD）和羟基神经酰胺的增加，但ncer2表现出自发细胞死亡（病原触发的PCD样-pPCD），并分别在35 d时LCB t18：0增加。NCER1功能的丧失导致茉莉酰基-异亮氨酸（JA-Ile）在叶片中积聚，而NCER2的破坏则伴随着更高水平的水杨酸（SA）和对伏马菌素B1（FB1）的敏感性增加。还发现所有突变体均能激活植物防御途径。这些数据强烈表明NCER1水解神经酰胺，而NCER2充当神经酰胺合酶。我们的研究结果揭示了NCER在这两个过程中植物激素和鞘脂水平之间的紧密联系中，在dPCD和pPCD的调节中起着重要作用。这些数据强烈表明NCER1水解神经酰胺，而NCER2充当神经酰胺合酶。我们的研究结果揭示了NCER在这两个过程中植物激素和鞘脂水平之间的紧密联系中，在dPCD和pPCD的调节中起着重要作用。这些数据强烈表明NCER1水解神经酰胺，而NCER2充当神经酰胺合酶。我们的研究结果揭示了NCER在这两个过程中植物激素和鞘脂水平之间的紧密联系中，在dPCD和pPCD的调节中起着重要作用。