The carboxy terminal transmembrane domain of SPL7 mediates interaction with RAN1 at the endoplasmic reticulum to regulate ethylene signaling in Arabidopsis

Jul.16,2022

Dr. Lei Li published a paper in New Phytologist.

In Arabidopsis, copper (Cu) transport to the ethylene receptor ETR1 mediated by RAN1, a Cu transporter located at the endoplasmic reticulum (ER), and Cu homeostasis mediated by SPL7, the key Cu-responsive transcription factor, are two deeply conserved vital processes. However, whether and how the two processes interact to regulate plant development remain elusive.
We found that its C-terminal transmembrane domain (TMD) anchors SPL7 to the ER, resulting in dual compartmentalization of the transcription factor. Immunoprecipitation coupled mass spectrometry, yeast two-hybrid, luciferase complementation imaging, and subcellular co-localization analyses indicate that SPL7 interacts with RAN1 at the ER via the TMD.
Genetic analysis revealed that ethylene-induced triple response was significantly compromised in the spl7 mutant, a phenotype rescuable by RAN1 over-expression but not by SPL7 without the TMD. The genetic interaction was corroborated by molecular analysis showing that SPL7 modulates RAN1 abundance in a TMD-dependent manner. Moreover, SPL7 is feedback-regulated by ethylene signaling via EIN3, which binds the SPL7 promoter and represses its transcription.
These results demonstrate that ER-anchored SPL7 constitutes a cellular mechanism to regulate RAN1 in ethylene signaling and lay the foundation for investigating how Cu homeostasis conditions ethylene sensitivity in the developmental context.