PUB46 and PUB48 E3 activities are only partially redundant under stress

The Arabidopsis E3s, PUB46, PUB47 and PUB48, are encoded by paralogous genes. Single pub46 and pub48 mutants display increased drought sensitivity compared to wild type (WT). The close proximity of the PUB46 and PUB48 genes precludes double mutants by crossing. However, an artificial microRNA (aMIR46-48) targeted to this subfamily reduced the activity of all three genes and resulted in increased drought sensitivity of WT plants. This phenotype resembled that of each single pub46 and pub48 mutant; in addition, the plants also showed enhanced sensitivity to methyl viologen, similar to that observed for pub46 single mutants. Moreover, WT plants expressing aMIR46-48 showed reduced inhibition by ABA at seed germination, a phenotype not observed in any of the single mutants. Expressing aMIR46-48 in pub46 and pub48 mutants further enhanced the drought sensitivity of each parental single mutant. Thus, whereas the gene-specific activity of the PUB46 and PUB48 E3s is partially redundant, absence of either E3 leading to drought sensitivity, our ability to eliminate the activity of both PUB46 and PUB48 in the same plant reveals additional gene-specific facets of their activity in the reaction to abiotic stress.