Fig 1.
Dynamic regulation of plant immunity through posttranslational modifications of NPR1.
Phosphorylation of NPR1 at serine 589 (S589) promotes nuclear localization of NPR1 monomers. At resting state (top panel), NPR1 can be phosphorylated at serine 55 and serine 59 (S55/59), which promotes its association with transcription factors (TF) that bind to repressive cis elements (- cis) in defense gene promoters. NPR1 that is not bound to—cis elements is targeted for degradation through SA-independent interaction with NPR4-CUL3 E3 ubiquitin ligases. As salicylic acid (SA) levels increase (bottom panel), NPR1 is sumoylated (S) and phosphorylated at serine 11 and serine 15 (S11/15), which switches its association with—cis elements to TFs bound to positive cis elements (+ cis) and activates defense genes. Transcriptionally active NPR1 is degraded through SA-dependent interaction with NPR3-CUL3 E3 ubiquitin ligase complexes to ensure full gene induction by refreshing the transcriptional machinery.