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Thulasi Devendrakumar K, Herrfurth C, Yeap M, Peng TS, Feussner I, Li X. Balancing roles between phosphatidylinositols and sphingolipids in regulating immunity and ER stress responses in pi4kβ1,2. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2024. [PMID: 39074039 DOI: 10.1111/tpj.16952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Revised: 06/08/2024] [Accepted: 07/16/2024] [Indexed: 07/31/2024]
Abstract
Plant immune regulation is complex. In addition to proteins, lipid molecules play critical roles in modulating immune responses. The mutant pi4kβ1,2 is mutated in two phosphatidylinositol 4-kinases PI4Kβ1 and β2 involved in the biosynthesis of phosphatidylinositol 4-phosphate (PI4P). The mutant displays autoimmunity, short roots, aberrant root hairs, and a heightened sensitivity to ER stress. In a forward genetic screen designed to dissect pi4kβ1,2 autoimmunity, we found that Orosomucoid-like 1 (ORM1) is required for the phenotypes of pi4kβ1,2, including short root and ER stress sensitivity. The orm1 mutations lead to increased long-chain base and ceramide levels in the suppressors. We also found that the basic region/leucine Zipper motif (bZIP) 28 and 60 transcription factors, central regulators of ER stress response, are required for its autoimmunity and root defect. In comparison, the defense-related phytohormones salicylic acid (SA) and N-hydroxypipecolic acid (NHP) are required for its autoimmunity but plays a minor role in its root phenotypes. Further, we found that wild-type plants overexpressing ORM1 are autoimmune, displaying short roots and increased ceramide levels. The autoimmunity of the ORM1 overexpression lines is dependent on SA, NHP, and bZIP60. As ORM1 is a known negative regulator of sphingolipid biosynthesis, our study uncovers a balancing role between PIs and sphingolipids in regulating immunity and ER stress responses in pi4kβ1,2.
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Affiliation(s)
- Karen Thulasi Devendrakumar
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
- Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
| | - Cornelia Herrfurth
- Albrecht-von-Haller-Institute for Plant Sciences, Department of Plant Biochemistry, University of Goettingen, Goettingen, D-37077, Germany
- Goettingen Center for Molecular Biosciences (GZMB), Service Unit for Metabolomics and Lipidomics, University of Goettingen, Goettingen, D-37077, Germany
| | - Mikaela Yeap
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
| | - Tony ShengZhe Peng
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
| | - Ivo Feussner
- Albrecht-von-Haller-Institute for Plant Sciences, Department of Plant Biochemistry, University of Goettingen, Goettingen, D-37077, Germany
- Goettingen Center for Molecular Biosciences (GZMB), Service Unit for Metabolomics and Lipidomics, University of Goettingen, Goettingen, D-37077, Germany
- Goettingen Center for Molecular Biosciences (GZMB), Department of Plant Biochemistry, University of Goettingen, Goettingen, D-37077, Germany
| | - Xin Li
- Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
- Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
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Fougère L, Mongrand S, Boutté Y. The function of sphingolipids in membrane trafficking and cell signaling in plants, in comparison with yeast and animal cells. Biochim Biophys Acta Mol Cell Biol Lipids 2024; 1869:159463. [PMID: 38281556 DOI: 10.1016/j.bbalip.2024.159463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 12/04/2023] [Accepted: 01/23/2024] [Indexed: 01/30/2024]
Abstract
Sphingolipids are essential membrane components involved in a wide range of cellular, developmental and signaling processes. Sphingolipids are so essential that knock-out mutation often leads to lethality. In recent years, conditional or weak allele mutants as well as the broadening of the pharmacological catalog allowed to decipher sphingolipid function more precisely in a less invasive way. This review intends to provide a discussion and point of view on the function of sphingolipids with a main focus on endomembrane trafficking, Golgi-mediated protein sorting, cell polarity, cell-to-cell communication and cell signaling at the plasma membrane. While our main angle is the plant field research, we will constantly refer to and compare with the advances made in the yeast and animal field. In this review, we will emphasize the role of sphingolipids not only as a membrane component, but also as a key player at a center of homeostatic regulatory networks involving direct or indirect interaction with other lipids, proteins and ion fluxes.
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Affiliation(s)
- Louise Fougère
- Laboratoire de Biogenèse Membranaire, Univ. Bordeaux, UMR 5200 CNRS, Villenave d'Ornon, France
| | - Sebastien Mongrand
- Laboratoire de Biogenèse Membranaire, Univ. Bordeaux, UMR 5200 CNRS, Villenave d'Ornon, France
| | - Yohann Boutté
- Laboratoire de Biogenèse Membranaire, Univ. Bordeaux, UMR 5200 CNRS, Villenave d'Ornon, France.
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Xi Y, Long X, Song M, Liu Y, Yan J, Lv Y, Yang H, Zhang Y, Miao W, Lin C. The fatty acid 2-hydroxylase CsSCS7 is a key hyphal growth factor and potential control target in Colletotrichum siamense. mBio 2024; 15:e0201523. [PMID: 38197633 PMCID: PMC10865788 DOI: 10.1128/mbio.02015-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 11/27/2023] [Indexed: 01/11/2024] Open
Abstract
SCS7 is a fatty acid 2-hydroxylase required for the synthesis of inositol phosphorylceramide but is not essential for normal growth in Saccharomyces cerevisiae. Here, we demonstrate that the Colletotrichum siamense SCS7 homolog CsSCS7 plays a key role in hyphal growth. The CsSCS7 deletion mutant showed strong hyphal growth inhibition, small conidia, and marginally reduced sporulation and also resulted in a sharp reduction in the full virulence and increasing the fungicide sensitivity. The three protein domains (a cytochrome b5 domain, a transmembrane domain, and a hydroxylase domain) are important to CsSCS7 protein function in hyphal growth. The fatty acid assay results revealed that the CsSCS7 gene is important for balancing the contents of multiple mid-long- and short-chain fatty acids. Additionally, the retarded growth and virulence of C. siamense ΔCsSCS7 can be recovered partly by the reintroduction of homologous sequences from Magnaporthe oryzae and Fusarium graminearum but not SCS7 of S. cerevisiae. In addition, the spraying of C. siamense with naked CsSCS7-double-stranded RNA (dsRNAs), which leads to RNAi, increases the inhibition of hyphal growth and slightly decreases disease lesions. Then, we used nano material Mg-Al-layered double hydroxide as carriers to deliver dsRNA, which significantly enhanced the control effect of dsRNA, and the lesion area was obviously reduced. These data indicated that CsSCS7 is an important factor for hyphal growth and affects virulence and may be a potential control target in C. siamense and even in filamentous plant pathogenic fungi.IMPORTANCECsSCS7, which is homologous to yeast fatty acid 2-hydroxylase SCS7, was confirmed to play a key role in the hyphal growth of Colletotrichum siamense and affect its virulence. The CsSCS7 gene is involved in the synthesis and metabolism of fatty acids. Homologs from the filamentous fungi Magnaporthe oryzae and Fusarium graminearum can recover the retarded growth and virulence of C. siamense ΔCsSCS7. The spraying of double-stranded RNAs targeting CsSCS7 can inhibit hyphal growth and reduce the disease lesion area to some extent. After using nano material Mg-Al layered double hydroxide as carrier, the inhibition rates were significantly increased. We demonstrated that CsSCS7 is an important factor for hyphal growth and affects virulence and may be a potential control target in C. siamense and even in filamentous plant pathogenic fungi.
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Affiliation(s)
- Yitao Xi
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Xiping Long
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Miao Song
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Yu Liu
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Jingting Yan
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Yanyun Lv
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Hong Yang
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
- Rubber Research Institute, Chinese Academy of Tropical Agricultural Science, Haikou, China
| | - Yu Zhang
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Weiguo Miao
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
| | - Chunhua Lin
- Sanya Institute of Breeding and Mutiplication, Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pest (Ministry of Education)/School of Tropical Agriculture and Forestry, Hainan University, Haikou, China
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Saucedo-García M, González-Solís A, Rodríguez-Mejía P, Lozano-Rosas G, Olivera-Flores TDJ, Carmona-Salazar L, Guevara-García AA, Cahoon EB, Gavilanes-Ruíz M. Sphingolipid Long-Chain Base Signaling in Compatible and Non-Compatible Plant-Pathogen Interactions in Arabidopsis. Int J Mol Sci 2023; 24:ijms24054384. [PMID: 36901815 PMCID: PMC10002605 DOI: 10.3390/ijms24054384] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Revised: 02/10/2023] [Accepted: 02/16/2023] [Indexed: 02/25/2023] Open
Abstract
The chemical diversity of sphingolipids in plants allows the assignment of specific roles to special molecular species. These roles include NaCl receptors for glycosylinositolphosphoceramides or second messengers for long-chain bases (LCBs), free or in their acylated forms. Such signaling function has been associated with plant immunity, with an apparent connection to mitogen-activated protein kinase 6 (MPK6) and reactive oxygen species (ROS). This work used in planta assays with mutants and fumonisin B1 (FB1) to generate varying levels of endogenous sphingolipids. This was complemented with in planta pathogenicity tests using virulent and avirulent Pseudomonas syringae strains. Our results indicate that the surge of specific free LCBs and ceramides induced by FB1 or an avirulent strain trigger a biphasic ROS production. The first transient phase is partially produced by NADPH oxidase, and the second is sustained and is related to programmed cell death. MPK6 acts downstream of LCB buildup and upstream of late ROS and is required to selectively inhibit the growth of the avirulent but not the virulent strain. Altogether, these results provide evidence that a LCB- MPK6- ROS signaling pathway contributes differentially to the two forms of immunity described in plants, upregulating the defense scheme of a non-compatible interaction.
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Affiliation(s)
- Mariana Saucedo-García
- Instituto de Ciencias Agropecuarias, Universidad Autónoma del Estado de Hidalgo, Tulancingo 43600, Mexico
| | - Ariadna González-Solís
- Department of Botany and Center for Quantitative Cell Imaging, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Priscila Rodríguez-Mejía
- Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, México City 04510, Mexico
| | - Guadalupe Lozano-Rosas
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México City 04510, Mexico
| | | | - Laura Carmona-Salazar
- Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, México City 04510, Mexico
| | - A. Arturo Guevara-García
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca 62210, Mexico
| | - Edgar B. Cahoon
- Center for Plant Science Innovation, Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE 68588, USA
| | - Marina Gavilanes-Ruíz
- Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, México City 04510, Mexico
- Correspondence:
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Altamura MM, Piacentini D, Della Rovere F, Fattorini L, Falasca G, Betti C. New Paradigms in Brassinosteroids, Strigolactones, Sphingolipids, and Nitric Oxide Interaction in the Control of Lateral and Adventitious Root Formation. PLANTS (BASEL, SWITZERLAND) 2023; 12:plants12020413. [PMID: 36679126 PMCID: PMC9864901 DOI: 10.3390/plants12020413] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 01/09/2023] [Accepted: 01/11/2023] [Indexed: 05/05/2023]
Abstract
The root system is formed by the primary root (PR), which forms lateral roots (LRs) and, in some cases, adventitious roots (ARs), which in turn may produce their own LRs. The formation of ARs is also essential for vegetative propagation in planta and in vitro and for breeding programs. Root formation and branching is coordinated by a complex developmental network, which maximizes the plant's ability to cope with abiotic stress. Rooting is also a response caused in a cutting by wounding and disconnection from the donor plant. Brassinosteroids (BRs) are steroid molecules perceived at the cell surface. They act as plant-growth-regulators (PGRs) and modulate plant development to provide stress tolerance. BRs and auxins control the formation of LRs and ARs. The auxin/BR interaction involves other PGRs and compounds, such as nitric oxide (NO), strigolactones (SLs), and sphingolipids (SPLs). The roles of these interactions in root formation and plasticity are still to be discovered. SLs are carotenoid derived PGRs. SLs enhance/reduce LR/AR formation depending on species and culture conditions. These PGRs possibly crosstalk with BRs. SPLs form domains with sterols within cellular membranes. Both SLs and SPLs participate in plant development and stress responses. SPLs are determinant for auxin cell-trafficking, which is essential for the formation of LRs/ARs in planta and in in vitro systems. Although little is known about the transport, trafficking, and signaling of SPLs, they seem to interact with BRs and SLs in regulating root-system growth. Here, we review the literature on BRs as modulators of LR and AR formation, as well as their crosstalk with SLs and SPLs through NO signaling. Knowledge on the control of rooting by these non-classical PGRs can help in improving crop productivity and enhancing AR-response from cuttings.
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Affiliation(s)
- Maria Maddalena Altamura
- Department of Environmental Biology, Sapienza University of Rome, 00185 Rome, Italy
- Correspondence:
| | - Diego Piacentini
- Department of Environmental Biology, Sapienza University of Rome, 00185 Rome, Italy
| | | | - Laura Fattorini
- Department of Environmental Biology, Sapienza University of Rome, 00185 Rome, Italy
| | - Giuseppina Falasca
- Department of Environmental Biology, Sapienza University of Rome, 00185 Rome, Italy
| | - Camilla Betti
- Department of Biosciences, University of Milan, 20133 Milan, Italy
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Goggin FL, Shah J, Gillaspy G. Editorial: Lipid metabolism and membrane structure in plant biotic interactions. FRONTIERS IN PLANT SCIENCE 2022; 13:1096268. [PMID: 36561441 PMCID: PMC9763929 DOI: 10.3389/fpls.2022.1096268] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 11/24/2022] [Indexed: 06/17/2023]
Affiliation(s)
- Fiona L. Goggin
- Department of Entomology and Plant Pathology, University of Arkansas System Division of Agriculture, Fayetteville, AR, United States
| | - Jyoti Shah
- Department of Biological Sciences and BioDiscovery Institute, University of North Texas, Denton, TX, United States
| | - Glenda Gillaspy
- College of Agriculture and Life Sciences, University of Wisconsin, Madison, WI, United States
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Lanubile A, De Michele R, Loi M, Fakhari S, Marocco A, Paciolla C. Cell death induced by mycotoxin fumonisin B 1 is accompanied by oxidative stress and transcriptional modulation in Arabidopsis cell culture. PLANT CELL REPORTS 2022; 41:1733-1750. [PMID: 35751667 PMCID: PMC9304057 DOI: 10.1007/s00299-022-02888-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/27/2022] [Accepted: 05/25/2022] [Indexed: 06/15/2023]
Abstract
Fumonisin B1 induces rapid programmed cell death in Arabidopsis cells, oxidative and nitrosative bursts, and differentially modulates cell death responsive genes. Glutathione is the main antioxidant involved in the stress response. Fumonisin B1 (FB1) is a fungal toxin produced by Fusarium spp. able to exert pleiotropic toxicity in plants. FB1 is known to be a strong inducer of the programmed cell death (PCD); however, the exact mechanism underling the plant-toxin interactions and the molecular events that lead to PCD are still unclear. Therefore, in this work, we provided a comprehensive investigation of the response of the model organism Arabidopsis thaliana at the nuclear, transcriptional, and biochemical level after the treatment with FB1 at two different concentrations, namely 1 and 5 µM during a time-course of 96 h. FB1 induced oxidative and nitrosative bursts and a rapid cell death in Arabidopsis cell cultures, which resembled a HR-like PCD event. Different genes involved in the regulation of PCD, antioxidant metabolism, photosynthesis, pathogenesis, and sugar transport were upregulated, especially during the late treatment time and with higher FB1 concentration. Among the antioxidant enzymes and compounds studied, only glutathione appeared to be highly induced in both treatments, suggesting that it might be an important stress molecule induced during FB1 exposure. Collectively, these findings highlight the complexity of the signaling network of A. thaliana and provide information for the understanding of the physiological, molecular, and biochemical responses to counteract FB1-induced toxicity.
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Affiliation(s)
- Alessandra Lanubile
- Department of Sustainable Crop Production, Università Cattolica del Sacro Cuore, via Emilia Parmense 84, 29122, Piacenza, Italy
| | - Roberto De Michele
- Institute of Biosciences and Bioresources, National Research Council of Italy, corso Calatafimi 414, 90129, Palermo, Italy.
| | - Martina Loi
- Institute of Sciences of Food Production, National Research Council of Italy, via Amendola 122/0, 70126, Bari, Italy
| | - Safieh Fakhari
- Institute of Biosciences and Bioresources, National Research Council of Italy, corso Calatafimi 414, 90129, Palermo, Italy
| | - Adriano Marocco
- Department of Sustainable Crop Production, Università Cattolica del Sacro Cuore, via Emilia Parmense 84, 29122, Piacenza, Italy
| | - Costantino Paciolla
- Department of Biology, Università degli Studi di Bari Aldo Moro, via E. Orabona 4, 70125, Bari, Italy.
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Groux R, Fouillen L, Mongrand S, Reymond P. Sphingolipids are involved in insect egg-induced cell death in Arabidopsis. PLANT PHYSIOLOGY 2022; 189:2535-2553. [PMID: 35608326 PMCID: PMC9342989 DOI: 10.1093/plphys/kiac242] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 05/04/2022] [Indexed: 05/05/2023]
Abstract
In Brassicaceae, hypersensitive-like programmed cell death (HR-like) is a central component of direct defenses triggered against eggs of the large white butterfly (Pieris brassicae). The signaling pathway leading to HR-like in Arabidopsis (Arabidopsis thaliana) is mainly dependent on salicylic acid (SA) accumulation, but downstream components are unclear. Here, we found that treatment with P. brassicae egg extract (EE) triggered changes in expression of sphingolipid metabolism genes in Arabidopsis and black mustard (Brassica nigra). Disruption of ceramide (Cer) synthase activity led to a significant decrease of EE-induced HR-like whereas SA signaling and reactive oxygen species levels were unchanged, suggesting that Cer are downstream activators of HR-like. Sphingolipid quantifications showed that Cer with C16:0 side chains accumulated in both plant species and this response was largely unchanged in the SA-induction deficient2 (sid2-1) mutant. Finally, we provide genetic evidence that the modification of fatty acyl chains of sphingolipids modulates HR-like. Altogether, these results show that sphingolipids play a key and specific role during insect egg-triggered HR-like.
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Affiliation(s)
- Raphaël Groux
- Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland
| | - Laetitia Fouillen
- Laboratoire de Biogénèse Membranaire, CNRS, UMR 5200, University of Bordeaux, F-33140 Villenave d’Ornon, France
| | - Sébastien Mongrand
- Laboratoire de Biogénèse Membranaire, CNRS, UMR 5200, University of Bordeaux, F-33140 Villenave d’Ornon, France
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Zeng HY, Bao HN, Chen YL, Chen DK, Zhang K, Liu SK, Yang L, Li YK, Yao N. The Two Classes of Ceramide Synthases Play Different Roles in Plant Immunity and Cell Death. FRONTIERS IN PLANT SCIENCE 2022; 13:824585. [PMID: 35463421 PMCID: PMC9021646 DOI: 10.3389/fpls.2022.824585] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 03/21/2022] [Indexed: 05/12/2023]
Abstract
Ceramide synthases (CSs) produce ceramides from long-chain bases (LCBs). However, how CSs regulate immunity and cell death in Arabidopsis thaliana 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 loh1-2 and loh1-1 loh3-1 mutants were resistant to the bacterial pathogen Pseudomonas syringae pv maculicola (Psm) DG3 and exhibited programmed cell death (PCD), along with increased LCBs and ceramides, at later stages. In loh1-2, the Psm 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 Psm, 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 via subtle control of LCBs and Cers in Arabidopsis.
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