Nagano Minoru, Kakuta Chikako, Fukao Yoichiro, Fujiwara Masayuki, Uchimiya Hirofumi, Kawai-Yamada Maki
Graduate School of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-8577, Japan.
Institute of Molecular and Cellular Biosciences, University of Tokyo, Bunkyo-ku, Tokyo, 113-0032, Japan.
J Plant Res. 2019 Jan;132(1):131-143. doi: 10.1007/s10265-018-01081-8. Epub 2019 Jan 2.
Bax inhibitor-1 (BI-1) is a widely conserved cell death regulator that confers resistance to environmental stress in plants. Previous studies suggest that Arabidopsis thaliana BI-1 (AtBI-1) modifies sphingolipids by interacting with cytochrome b (AtCb5), an electron-transfer protein. To reveal how AtBI-1 regulates sphingolipid synthesis, we screened yeast sphingolipid-deficient mutants and identified yeast ELO2 and ELO3 as novel enzymes that are essential for AtBI-1 function. ELO2 and ELO3 are condensing enzymes that synthesize very-long-chain fatty acids (VLCFAs), major fatty acids in plant sphingolipids. In Arabidopsis, we identified four ELO homologs (AtELO1-AtELO4), localized in the endoplasmic reticulum membrane. Of those AtELOs, AtELO1 and AtELO2 had a characteristic histidine motif and were bound to AtCb5-B. This result suggests that AtBI-1 interacts with AtELO1 and AtELO2 through AtCb5. AtELO2 and AtCb5-B also interact with KCR1, PAS2, and CER10, which are essential for the synthesis of VLCFAs. Therefore, AtELO2 may participate in VLCFA synthesis with AtCb5 in Arabidopsis. In addition, our co-immunoprecipitation/mass spectrometry analysis demonstrated that AtBI-1 forms a complex with AtELO2, KCR1, PAS2, CER10, and AtCb5-D. Furthermore, AtBI-1 contributes to the rapid synthesis of 2-hydroxylated VLCFAs in response to oxidative stress. These results indicate that AtBI-1 regulates VLCFA synthesis by interacting with VLCFA-synthesizing enzymes.
Bax抑制剂-1（BI-1）是一种广泛保守的细胞死亡调节因子，可赋予植物对环境胁迫的抗性。先前的研究表明，拟南芥BI-1（AtBI-1）通过与电子传递蛋白细胞色素b（AtCb5）相互作用来修饰鞘脂。为了揭示AtBI-1如何调节鞘脂合成，我们筛选了酵母鞘脂缺陷型突变体，并鉴定出酵母ELO2和ELO3是AtBI-1功能所必需的新酶。ELO2和ELO3是合成超长链脂肪酸（VLCFA）的缩合酶，VLCFA是植物鞘脂中的主要脂肪酸。在拟南芥中，我们鉴定出四个ELO同源物（AtELO1-AtELO4），它们定位于内质网膜。在这些AtELO中，AtELO1和AtELO2具有特征性的组氨酸基序，并与AtCb5-B结合。这一结果表明AtBI-1通过AtCb5与AtELO1和AtELO2相互作用。AtELO2和AtCb5-B还与KCR1、PAS2和CER10相互作用，它们是VLCFA合成所必需的。因此，AtELO2可能在拟南芥中与AtCb5一起参与VLCFA的合成。此外，我们的免疫共沉淀/质谱分析表明，AtBI-1与AtELO2、KCR1、PAS2、CER10和AtCb5-D形成复合物。此外，AtBI-1有助于响应氧化应激快速合成2-羟基化的VLCFA。这些结果表明，AtBI-1通过与VLCFA合成酶相互作用来调节VLCFA的合成。
