Mutations in SUMO conjugating enzyme reveal contributions of sumoylation to plant stress resilience and yield.

Small ubiquitin-related modifier (SUMO) conjugation is a fundamental process in all metazoa, with multiple roles in development and stress responses. In Arabidopsis thaliana and many other dicots, the SUMO conjugating enzyme (SCE) is a single-copy gene, making it a linchpin in all transcriptional and posttranscriptional processes influenced by sumoylation. Loss of function of Arabidopsis SCE1 is lethal, but we were able to generate a hypomorphic (decrease-of-function; sce1-100) and a hypermorphic (increase-of-function; SCE1 K28R) allele of this gene. The hypomorphic allele has traits in common with a mutant defective in SUMO ligase SIZ1, compromising development and stress resilience. We compare transcriptional responses of sce1-100 and siz1 and define processes that depend on SUMO but are independent of salicylic acid, a plant hormone that accumulates upon a decrease in sumoylation. The hypermorphic allele SCE1 K28R impacts on plants under normal glasshouse conditions, leading to higher seed yield. Under the stress of low nitrogen supply, these plants show increased root foraging, facilitating nitrogen uptake under limiting conditions. The two SCE1 mutant alleles provide a valuable framework for uncovering processes with SUMO participation. Due to their NGT1 (non-transgenic) legal status, experiments outside transgene confinement facilities will be possible with these mutants.