The plant hormone ethylene promotes abiotic stress tolerance in the liverwort .

Plants are often faced with an array of adverse environmental conditions and must respond appropriately to grow and develop. In angiosperms, the plant hormone ethylene is known to play a protective role in responses to abiotic stress. Here we investigated whether ethylene mediates resistance to abiotic stress in the liverwort , one of the most distant land plant relatives of angiosperms. Using existing knockout mutants of Mp, and Mp, two genes in the ethylene signaling pathway, we examined responses to heat, salinity, nutrient deficiency, and continuous far-red light. The Mp and Mp mutants were previously shown to confer ethylene insensitivity and constitutive ethylene responses, respectively. Using mild or sub-lethal doses of each stress treatment, we found that Mp mutants displayed stress resilience similar to or greater than the wild type. In contrast, Mp mutants showed less resilience than the wild type. Consistent with ethylene being a stress hormone, we demonstrated that ethylene production is enhanced by each stress treatment. These results suggest that ethylene plays a role in protecting against abiotic stress in , and that ethylene has likely been conserved as a stress hormone since before the evolutionary divergence of bryophytes from the land plant lineage approximately 450 Ma.