The Two Classes of Ceramide Synthases Play Different Roles in Plant Immunity and Cell Death

Abstract

Ceramide synthases (CSs) produce ceramides from long-chain bases (LCBs). However, how CSs regulate immunity and cell death in <i>Arabidopsis thaliana</i> remains unclear. Here, we decipher the roles of two classes of CS, CSI (LAG1 HOMOLOG 2, LOH2) and CSII (LOH1/3), in these processes. The <i>loh1-2</i> and <i>loh1-1 loh3-1</i> mutants were resistant to the bacterial pathogen <i>Pseudomonas syringae</i> pv <i>maculicola</i> (<i>Psm</i>) DG3 and exhibited programmed cell death (PCD), along with increased LCBs and ceramides, at later stages. In <i>loh1-2</i>, the <i>Psm</i> resistance, PCD, and sphingolipid accumulation were mostly suppressed by inactivation of the lipase-like proteins ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN DEFICIENT 4 (PAD4), and partly suppressed by loss of SALICYLIC ACID INDUCTION DEFICIENT 2 (SID2). The LOH1 inhibitor fumonisin B1 (FB1) triggered EDS1/PAD4-independent LCB accumulation, and EDS1/PAD4-dependent cell death, resistance to <i>Psm</i>, and C16 Cer accumulation. Loss of LOH2 enhances FB1-, and sphinganine-induced PCD, indicating that CSI negatively regulates the signaling triggered by CSII inhibition. Like Cer, LCBs mediate cell death and immunity signaling, partly through the EDS1/PAD4 pathway. Our results show that the two classes of ceramide synthases differentially regulate EDS1/PAD4-dependent PCD and immunity <i>via</i> subtle control of LCBs and Cers in Arabidopsis.