Ubiquitination steers SRF3 plasma membrane nano-organization to specify signaling outputs

Organisms cope with myriads of competing and conflicting environmental signals. These signals are often perceived by cell surface receptor kinases to mount appropriate adaptive responses. However, it is not well understood by which mechanism single receptor kinases can transduce different signals. The plant receptor kinase SRF3 transduces low iron and bacteria-derived signals. We found that upon these signals, ubiquitinated SRF3 is recognized by clathrin-mediated endocytosis for vacuolar targeting. Live super resolution microscopy revealed that cell surface SRF3 is present in a fast diffusible fraction, which is sustained by ubiquitination, and that non-ubiquitinated SRF3 is present in immobile nanodomains. Ubiquitination-mediated degradation of SRF3 is required for signaling only under low iron but not upon flg22 perception. Flg22-triggered SRF3 phosphorylation leads to SRF3 accumulation in the immobile fraction in which degradation is restricted, thereby preventing low iron signaling. We therefore propose that ubiquitination-dependent plasma membrane nano-organization of SRF3 specifies its signal transduction pathways.