HOS1 ubiquitinates SPL9 for degradation to modulate salinity-delayed flowering.

Soil salinity is a serious environmental threat to plant growth and flowering. Flowering in the right place, at the right time, ensures maximal reproductive success for plants. Salinity-delayed flowering is considered a stress coping/survival strategy and the molecular mechanisms underlying this process require further studies to enhance the crop's salt tolerance ability. A nuclear pore complex (NPC) component, HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 1 (HOS1), has been recognized as a negative regulator of plant cold responses and flowering. Here, we challenged the role of HOS1 in regulating flowering in response to salinity stress. Interestingly, we discovered that HOS1 can directly interact with and ubiquitinate transcription factor SPL9 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9) to promote its protein degradation in response to salinity stress. Moreover, we demonstrated that HOS1 and SPL9 antagonistically regulate plant flowering under both normal and salt stress conditions. HOS1 was further shown to negatively regulate the expression of SPLs and several key flowering genes in response to salinity stress. These results jointly revealed that HOS1 is an important integrator in the process of modulating salinity-delayed flowering, thus offering new perspectives on a salinity stress coping strategy of plants.