Overexpression of Arabidopsis ubiquitin ligase AtPUB46 enhances tolerance to drought and oxidative stress

•Overexpressing of the AtPUB46 gene encoding ubiquitin ligase increased plant tolerance to drought.•Germination of AtPUB46-OE plants is not affected by inhibitory salt concentrations.•Greening of AtPUB46-OE seedlings is hypersensitive to salt, but hyposensitive to methyl viologen induced oxidative stress.•Leaves of AtPUB46-OE plants have reduced stomatal index and pore area but unaltered stomatal density and rate of water loss.•AtPUB46 is mostly localized in the cytosol, and enters the nucleus following exposure to H2O2. The U-Box E3 ubiquitin ligase, AtPUB46, functions in the drought response: T-DNA insertion mutants of this single paralogous gene are hypersensitive to water- and oxidative stress (Adler et al. BMC Plant Biology 17:8, 2017). Here we analyze the phenotype of AtPUB46 overexpressing (OE) plants. AtPUB46-OE show increased tolerance to water stress and have smaller leaf blades and reduced stomatal pore area and stomatal index compared with wild type (WT). Despite this, the rate of water loss from detached rosettes is similar in AtPUB46-OE and WT plants. Germination of AtPUB46-OE seeds was less sensitive to salt than WT whereas seedling greening was more sensitive. We observed a complex response to oxidative stress applied by different agents: AtPUB46-OE plants were hypersensitive to H2O2 but hyposensitive to methyl viologen. AtPUB46-GFP fusion protein is cytoplasmic, however, in response to H2O2 a considerable proportion translocates to the nucleus. We conclude that the differential stress phenotype of the AtPUB46-OE does not result from its smaller leaf size but from a change in the activity of a stress pathway(s) regulated by a degradation substrate of the AtPUB46 E3 and also from a reduction in stomatal pore size and index.