Xin Liu, Linlin Song, Heng Zhang, Yijuan Lin, Xiaolei Shen, Jiayuan Guo, Meiling Su, Gaosheng Shi, Zonghua Wang, Guo-Dong Lu

Molecular Plant Pathology 30 August 2021; on line https://doi.org/10.1111/mpp.13132

Abstract

The functions of ubiquitin-conjugating enzymes (E2) in plant immunity are not well understood. In this study, OsUBC26, a rice ubiquitin-conjugating enzyme, was characterized in the defence against Magnaporthe oryzae. The expression of OsUBC26 was induced by M. oryzae inoculation and methyl jasmonate treatment. Both RNA interference lines and CRISPR/Cas9 null mutants of OsUBC26 reduced rice resistance to M. oryzae. WRKY45 was down-regulated in OsUBC26 null mutants. In vitro E2 activity assay indicated that OsUBC26 is an active ubiquitin-conjugating enzyme. Yeast two-hybrid assays using OsUBC26 as bait identified the RING-type E3 ligase UCIP2 as an interacting protein. Coimmunoprecipitation assays confirmed the interaction between OsUBC26 and UCIP2. The CRISPR/Cas9 mutants of UCIP2 also showed compromised resistance to M. oryzae. Yeast two-hybrid screening using UCIP2 as bait revealed that APIP6 is a binding partner of UCIP2. Moreover, OsUBC26 working with APIP6 ubiquitinateds AvrPiz-t, an avirulence effector of M. oryzae, and OsUBC26 null mutation impaired the proteasome degradation of AvrPiz-t in rice cells. In summary, OsUBC26 plays important roles in rice disease resistance by regulating WRKY45 expression and working with E3 ligases such as APIP6 to counteract the effector protein AvrPiz-t from M. oryzae.

See https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/mpp.13132

Figure 7: OsUBC26 could work with APIP6 and ubiquitinate AvrPiz-t in vitro. (a) Schematic representation of the plasmids pCDFDuet-MBP-AvrPiz-t-HA-AtUBA1-S, pACYCDuet-APIP6-Myc-OsUBC26-S, and pET-28a-FLAG-UBQ. (b) Detection of ubiquitination of AvrPiz-t. The crude total proteins were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and visualized by western blot with corresponding antibodies.