SUMO proteases OTS1 and 2 control filament elongation through a DELLA-dependent mechanism

During fertilization, stamen elongation needs tobe synchronized with pistil growth. The phytohormonegibberellic acid (GA) promotes stamen growth by stimu-lating the degradation of growth repressing DELLA pro-teins. DELLA accumulation is negatively regulated byGAs through the ubiquitin–proteasome system. In Ara-bidopsis thaliana, a proportion of DELLAs is also conju-gated to the small ubiquitin-like modifier (SUMO) protein,which stabilizes DELLAs. Increased DELLA levels occurin the SUMO protease-deficient OVERLY TOLERANT TOSALT 1 and 2 (ots1 ots2 ) double mutants, especially undersalt stress conditions. Here, we show that OTS genes play aredundant role in the control of plant fertility under non-stress conditions. Mutants of ots1 ots2 display reducedfertility compared with the wild type, owing to reducedstamen elongation. Stamen growth, pollination rate andseed production are restored in ots1 ots2 della mutants,thus linking OTS1 function to the control of DELLAactivity in the context of filament elongation. OTS levelsappear to be developmentally regulated as OTS1/2 tran-script upregulation during stamen development overlapswith GAs accumulations. We propose that OTS genesenable synchronization of stamen development by facili-tating DELLA degradation at a specific developmentalstage.