Mural Ravi V, Liu Yao, Rosebrock Tracy R, Brady Jennifer J, Hamera Sadia, Connor Richard A, Martin Gregory B, Zeng Lirong
Biology Department, University of Arkansas, Little Rock, Arkansas 72204.
Plant Cell. 2013 Sep;25(9):3615-31. doi: 10.1105/tpc.113.117093. Epub 2013 Sep 27.
The activation of an immune response in tomato (Solanum lycopersicum) against Pseudomonas syringae relies on the recognition of E3 ligase-deficient forms of AvrPtoB by the host protein kinase, Fen. To investigate the mechanisms by which Fen-mediated immunity is regulated, we characterize in this study a Fen-interacting protein, Fni3, and its cofactor, S. lycoperiscum Uev (Suv). Fni3 encodes a homolog of the Ubc13-type ubiquitin-conjugating enzyme that catalyzes exclusively Lys-63-linked ubiquitination, whereas Suv is a ubiquitin-conjugating enzyme variant. The C-terminal region of Fen was necessary for interaction with Fni3, and this interaction was required for cell death triggered by overexpression of Fen in Nicotiana benthamiana leaves. Fni3 was shown to be an active E2 enzyme, but Suv displayed no ubiquitin-conjugating activity; Fni3 and Suv together directed Lys-63-linked ubiquitination. Decreased expression of Fni3, another tomato Ubc13 homolog, Sl-Ubc13-2, or Suv in N. benthamiana leaves diminished cell death associated with Fen-mediated immunity and cell death elicited by several other resistance (R) proteins and their cognate effectors. We also discovered that coexpression of Fen and other R proteins/effectors with a Fni3 mutant that is compromised for ubiquitin-conjugating activity diminished the cell death. These results suggest that Fni3/Sl-Ubc13-2 and Suv regulate the immune response mediated by Fen and other R proteins through Lys-63-linked ubiquitination.
番茄（Solanum lycopersicum）对丁香假单胞菌（Pseudomonas syringae）免疫反应的激活依赖于宿主蛋白激酶Fen对E3连接酶缺陷型AvrPtoB的识别。为了研究Fen介导的免疫调节机制，我们在本研究中鉴定了一种与Fen相互作用的蛋白Fni3及其辅助因子番茄Uev（Suv）。Fni3编码一种Ubc13型泛素结合酶的同源物，该酶仅催化K63连接的泛素化，而Suv是一种泛素结合酶变体。Fen的C末端区域对于与Fni3相互作用是必需的，并且这种相互作用是本氏烟草叶片中Fen过表达引发细胞死亡所必需的。Fni3被证明是一种活性E2酶，但Suv没有泛素结合活性；Fni3和Suv共同指导K63连接的泛素化。本氏烟草叶片中Fni3、另一种番茄Ubc13同源物Sl-Ubc13-2或Suv表达的降低减少了与Fen介导的免疫相关的细胞死亡以及由其他几种抗性（R）蛋白及其同源效应子引发的细胞死亡。我们还发现，Fen和其他R蛋白/效应子与泛素结合活性受损的Fni3突变体共表达会减少细胞死亡。这些结果表明，Fni3/Sl-Ubc13-2和Suv通过K63连接的泛素化调节Fen和其他R蛋白介导的免疫反应。
