The SUMO E3 Ligase SIZ1 Negatively Regulates Shoot Regeneration

Abstract

Plants form calluses and regenerate new organs when incubated on phytohormone-containing media. While accumulating evidence suggests that these regenerative processes are governed by transcriptional networks orchestrating wound response and developmental transitions, it remains unknown if posttranslational regulatory mechanisms are involved in this process. In this study, we demonstrate that SAP AND MIZ1 DOMAIN- CONTAINING LIGASE1 (SIZ1), an E3 ligase-catalyzing attachment of the SMALL UBIQUITIN-LIKE MODIFIER (SUMO) to proteins, regulates wound-induced signal transduction and organ regeneration in Arabidopsis (<i>Arabidopsis thaliana</i>). We show that loss-of-function mutants for <i>SIZ1</i> exhibit overproduction of shoot meristems under in vitro tissue culture conditions, while this defect is rescued in a complementation line expressing <i>pSIZ1</i>::<i>SIZ1</i> RNA sequencing analysis revealed that <i>siz1-2</i> mutants exhibit enhanced transcriptional responses to wound stress, resulting in the hyper-induction of over 400 genes immediately after wounding. Among them, we show that elevated levels of <i>WOUND INDUCED DEDIFFERENTIATION1</i> (<i>WIND1</i>) and <i>WIND2</i> contribute to the enhanced shoot regeneration observed in <i>siz1</i> mutants, as expression of the dominant-negative chimeric protein WIND1-SRDX (SUPERMAN repression domain) in <i>siz1-3</i> mutants partly rescues this phenotype. Although compromised <i>SIZ1</i> function does not modify the transcription of genes implicated in auxin-induced callus formation and/or pluripotency acquisition, it does lead to enhanced induction of cytokinin-induced shoot meristem regulators such as <i>WUSCHEL</i>, promoting the formation of <i>WUSCHEL</i>-expressing foci in explants. This study thus suggests that SIZ1 negatively regulates shoot regeneration in part by repressing wound-induced developmental reprogramming.