SUMO enables substrate selectivity by mitogen-activated protein kinases to regulate immunity in plants

Abstract

The versatility of mitogen-activated protein kinases (MAPKs) in translating exogenous and endogenous stimuli into appropriate cellular responses depends on its substrate specificity. In animals, several mechanisms have been proposed about how MAPKs maintain specificity to regulate distinct functional pathways. However, little is known of mechanisms that enable substrate selectivity in plant MAPKs. Small ubiquitin-like modifier (SUMO), a posttranslational modification system, plays an important role in plant development and defense by rapid reprogramming of cellular events. In this study we identified a functional SUMO interaction motif (SIM) in Arabidopsis MPK3 and MPK6 that reveals a mechanism for selective interaction of MPK3/6 with SUMO-conjugated WRKY33, during defense. We show that WRKY33 is rapidly SUMOylated in response to Botrytis cinerea infection and flg22 elicitor treatment. SUMOylation mediates WRKY33 phosphorylation by MPKs and consequent transcription factor activity. Disruption of either WRKY33 SUMO or MPK3/6 SIM sites attenuates their interaction and inactivates WRKY33-mediated defense. However, MPK3/6 SIM mutants show normal interaction with a non-SUMOylated form of another transcription factor, SPEECHLESS, unraveling a role for SUMOylation in differential substrate selectivity by MPKs. We reveal that the SUMO proteases, SUMO PROTEASE RELATED TO FERTILITY1 (SPF1) and SPF2 control WRKY33 SUMOylation and demonstrate a role for these SUMO proteases in defense. Our data reveal a mechanism by which MPK3/6 prioritize molecular pathways by differentially selecting substrates using the SUMO–SIM module during defense responses.

MAP kinase cascades in plant development and immune signaling

“…Post‐translational modifications of substrates are also involved in regulating their interactions with MAPKs and affect the specificity of MAPK signaling. For example, WRKY33 undergoes rapid SUMOylation in response to Botrytis cinerea infection or flg22 treatment, which enables its association with MPK3/6 during plant immunity (Verma et al , 2021). The SUMO interaction motif (SIM) present in MPK3/6 is required for their interactions with WRKY33 and phosphorylation of WRKY33, but is dispensable for the association with the non‐SUMOylation form of another substrate, SPCH, supporting a role for SUMOylation in substrate selectivity by MAPKs (Verma et al , 2021).…”

SUMOylation of different targets fine‐tunes phytochrome signaling

“…For example, phyB, COP1, PIF3 and FHY1 are also phosphorylated and their phosphorylation modifies photomorphogenesis (Shen et al ., 2009; Chen et al ., 2012; Ni et al ., 2013, 2017; Lin et al ., 2017; Viczián et al ., 2020). We have to note, however, that the interplay of phosphorylation and SUMOylation of these proteins is not studied, and despite recent advances (Verma et al ., 2021) our general knowledge about the coordinated action of these PTMs on the biological activity of a target protein is rather limited. Similarly, we do not know how the interplay of SUMOylation and ubiquitination can modify light signaling, although, based on reports from other experimental systems, we might expect future studies focusing on this subject (Lamoliatte et al ., 2017; Rott et al ., 2017).…”

Understanding and Exploiting Post-Translational Modifications for Plant Disease Resistance

“…Several WRKYs were identified as targets of SUMO1 by proteomics, as well as MAPK phosphorylation [104]. To support this, it was exhibited that in response to Botrytis cinerea infection and flg22 elicitor treatment, WRKY33 is SUMOylated, which allows WRKY33 phosphorylation by MPK3/6 for activation of transcription factor activity leading to increased camalexin biosynthesis (Figure 1) [138].…”