Membrane protein MHZ3 stabilizes OsEIN2 in rice by interacting with its Nramp-like domain

Proc Natl Acad Sci U S A. 2018 Mar 6;115(10):2520-2525. doi: 10.1073/pnas.1718377115. Epub 2018 Feb 20.

Abstract

The phytohormone ethylene regulates many aspects of plant growth and development. EIN2 is the central regulator of ethylene signaling, and its turnover is crucial for triggering ethylene responses. Here, we identified a stabilizer of OsEIN2 through analysis of the rice ethylene-response mutant mhz3. Loss-of-function mutations lead to ethylene insensitivity in etiolated rice seedlings. MHZ3 encodes a previously uncharacterized membrane protein localized to the endoplasmic reticulum. Ethylene induces MHZ3 gene and protein expression. Genetically, MHZ3 acts at the OsEIN2 level in the signaling pathway. MHZ3 physically interacts with OsEIN2, and both the N- and C-termini of MHZ3 specifically associate with the OsEIN2 Nramp-like domain. Loss of mhz3 function reduces OsEIN2 abundance and attenuates ethylene-induced OsEIN2 accumulation, whereas MHZ3 overexpression elevates the abundance of both wild-type and mutated OsEIN2 proteins, suggesting that MHZ3 is required for proper accumulation of OsEIN2 protein. The association of MHZ3 with the Nramp-like domain is crucial for OsEIN2 accumulation, demonstrating the significance of the OsEIN2 transmembrane domains in ethylene signaling. Moreover, MHZ3 negatively modulates OsEIN2 ubiquitination, protecting OsEIN2 from proteasome-mediated degradation. Together, these results suggest that ethylene-induced MHZ3 stabilizes OsEIN2 likely by binding to its Nramp-like domain and impeding protein ubiquitination to facilitate ethylene signal transduction. Our findings provide insight into the mechanisms of ethylene signaling.

Keywords: ethylene; protein stabilization; protein–protein interaction; rice.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ethylenes / metabolism
  • Etiolation
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mutation
  • Oryza / genetics
  • Oryza / metabolism*
  • Plant Growth Regulators / metabolism
  • Plant Proteins / chemistry
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / metabolism*
  • Protein Domains
  • Seedlings / genetics
  • Seedlings / metabolism
  • Signal Transduction / genetics
  • Signal Transduction / physiology

Substances

  • Ethylenes
  • Membrane Proteins
  • Plant Growth Regulators
  • Plant Proteins
  • ethylene