Post-translational modification of proteins by attachment of small ubiquitin-like modifier (SUMO) is essential for plant growth and development. Mutations in the SUMO protease early in short days 4 (ESD4) cause hyperaccumulation of conjugates formed between SUMO and its substrates, and phenotypically are associated with extreme early flowering and impaired growth. We performed a suppressor mutagenesis screen ofesd4and identified a series of mutants calledsuppressor of esd4(sed), which delay flowering, enhance growth and reduce hyperaccumulation of SUMO conjugates. Genetic mapping and genome sequencing indicated that one of these mutations (sed111) is in the gene salicylic acid induction-deficient 2 (SID2), which encodes ISOCHORISMATE SYNTHASE I, an enzyme required for biosynthesis of salicylic acid (SA). Analyses showed that compared with wild-type plants,esd4contains higher levels ofSID2mRNA and about threefold more SA, whereassed111contains lower SA levels. Othersedmutants also contain lower SA levels but are not mutant forSID2, although most reduceSID2mRNA levels. Therefore, higher SA levels contribute to the small size, early flowering and elevated SUMO conjugate levels ofesd4. Our results support previous data indicating that SUMO homeostasis influences SA biosynthesis in wild-type plants, and also demonstrate that elevated levels of SA strongly increase the abundance of SUMO conjugates.