Goemann, J. | Search bioRxiv

bioRxiv2021

Sphingolipid-Induced Programmed Cell Death Is a Salicylic Acid and EDS1-Dependent Phenotype in Arabidopsis

Ceramides and long chain bases (LCBs) are plant sphingolipids involved in the induction of plant programmed cell death (PCD). The fatty acid hydroxylase mutant fah1 fah2 exhibits high ceramide levels and moderately elevated LCB levels. Salicylic acid (SA) is strongly induced in these mutants, but no cell death is visible. To determine the effect of ceramides with different chain lengths, fah1 fah2 was crossed with ceramide synthase mutants longevity assurance gene one homologue1-3 (loh1, loh2 and loh3). Surprisingly, only triple mutants with loh2 show a cell death phenotype under the selected conditions. Sphingolipid profiling revealed that the greatest differences between the triple mutant plants are in the LCB and LCB-phosphate (LCB-P) fraction. fah1 fah2 loh2 plants accumulate LCB d18:0 and LCB-P d18:0. Crossing fah1 fah2 loh2 with the SA synthesis mutant sid2-2, and with the SA signaling mutants enhanced disease susceptibility 1-2 (eds1-2) and phytoalexin deficient 4-1 (pad4-1), revealed that lesions are SA- and EDS1-dependent. These quadruple mutants also suggest that there may be a feedback loop between SA and sphingolipid metabolism as they accumulated less ceramides and LCBs. In conclusion, PCD in fah1 fah2 loh2 is a SA and EDS1-dependent phenotype, which is likely due to accumulation of LCB d18:0.

biochemistry↗

bioRxiv2019

Mps1 releases Mad1 from nuclear pores to ensure a robust mitotic checkpoint and accurate chromosome segregation

The strength of the Spindle Assembly Checkpoint (SAC) depends on the amount of the Mad1-C-Mad2 heterotetramer at kinetochores but also on its binding to Megator/Tpr at nuclear pore complexes (NPCs) during interphase. However, the molecular underpinnings controlling the spatiotemporal redistribution of Mad1-C-Mad2 as cells progress into mitosis remain elusive. Here, we show that Mps1-mediated phosphorylation of Megator/Tpr abolishes its interaction with Mad1 in vitro and in Drosophila cells. Timely activation of Mps1 during prophase triggers Mad1 release from NPCs, which we find to be required for competent kinetochore recruitment of Mad1-C-Mad2 and robust checkpoint response. Importantly, preventing Mad1 binding to Megator/Tpr rescues the fidelity of chromosome segregation and aneuploidy in larval neuroblasts of Drosophila mps1-null mutants. Our findings demonstrate that the subcellular localization of Mad1 is stringently coordinated with cell cycle progression by kinetochore-extrinsic activity of Mps1. This ensures that both NPCs in interphase and kinetochores in mitosis can generate anaphase inhibitors to efficiently preserve genomic stability.

cell biology↗