title: A conserved cysteine motif is critical for rice ceramide kinase activity and function.
abstract: BACKGROUND
  Ceramide kinase (CERK) is a key regulator of cell survival in dicotyledonous plants and animals. Much less is known about the roles of CERK and ceramides in mediating cellular processes in monocot plants. Here, we report the characterization of a ceramide kinase, OsCERK, from rice (Oryza sativa spp. Japonica cv. Nipponbare) and investigate the effects of ceramides on rice cell viability.
  
  
  RESULTS
  OsCERK can complement the Arabidopsis CERK mutant acd5. Recombinant OsCERK has ceramide kinase activity with Michaelis-Menten kinetics and optimal activity at 7.0 pH and 40°C. Mg2+ activates OsCERK in a concentration-dependent manner. Importantly, a CXXXCXXC motif, conserved in all ceramide kinases and important for the activity of the human enzyme, is critical for OsCERK enzyme activity and in planta function. In a rice protoplast system, inhibition of CERK leads to cell death and the ratio of added ceramide and ceramide-1-phosphate, CERK's substrate and product, respectively, influences cell survival. Ceramide-induced rice cell death has apoptotic features and is an active process that requires both de novo protein synthesis and phosphorylation, respectively. Finally, mitochondria membrane potential loss previously associated with ceramide-induced cell death in Arabidopsis was also found in rice, but it occurred with different timing.
  
  
  CONCLUSIONS
  OsCERK is a bona fide ceramide kinase with a functionally and evolutionarily conserved Cys-rich motif that plays an important role in modulating cell fate in plants. The vital function of the conserved motif in both human and rice CERKs suggests that the biochemical mechanism of CERKs is similar in animals and plants. Furthermore, ceramides induce cell death with similar features in monocot and dicot plants.
authors.affiliation: State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
authors.forename: Fang-Cheng
authors.initials: FC
authors.lastname: Bi
authors.forename: Quan-Fang
authors.initials: QF
authors.lastname: Zhang
authors.forename: Zhe
authors.initials: Z
authors.lastname: Liu
authors.forename: Ce
authors.initials: C
authors.lastname: Fang
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.forename: Jian-Bin
authors.initials: JB
authors.lastname: Su
authors.forename: Jean T
authors.initials: JT
authors.lastname: Greenberg
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Wang
authors.forename: Nan
authors.initials: N
authors.lastname: Yao
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics / Q000502:physiology; D003545:Cysteine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000201:enzymology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D010940:Plant Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C066324:ceramide kinase; D003545:Cysteine