Possible modulation of Arabidopsis ETR1 N-terminal signaling by CTR1

The mitogen-activated protein kinase kinase kinase (MA PKKK) constitutive triple-response1 (CTR 1) plays a key role in mediating ethylene receptor signaling via its N-terminal interaction with the ethylene receptor C-terminal histidine kinase (HK) domain. Loss-of-function mutations of CTR1 prevent ethylene receptor signaling, and corresponding ctr1 mutants show a constitutive ethylene response phenotype. We recently reported in Plant Physiology that expression of the truncated ethylene receptor Ethylene Response1 (ETR 1) isoforms etr11-349 and dominant ethylene-insensitive etr1-11-349, lacking the C-terminal HK and receiver domains, both suppressed the ctr1 mutant phenotype. Therefore, the ETR 1 N terminus is capable of receptor signaling independent of CTR 1. The constitutive ethylene response phenotype is stronger for ctr1-1 than ctr1-1 lines expressing the etr11-349 transgene, so N-terminal signaling by the full-length but not truncated ETR 1 is inhibited by ctr1-1. We address possible modulations of ETR 1 N-terminal signaling with docking of CTR 1 on the ETR 1 HK domain.