The Activity of the Stress Modulated Arabidopsis Ubiquitin Ligases PUB46 and PUB48 is Partially Redundant

The Arabidopsis ubiquitin ligases PUB46, PUB47 and PUB48 are encoded by paralogus genes; pub46 and pub48 mutants display increased drought sensitivity compared to wild type (WT). Although the phenotype displayed in the single gene mutants, suggest that each has specific biological activity, PUB46 and PUB48 activity may be also redundant. To test functional redundancy between two gene products requires a double mutant. Unfortunately, the close proximity of the PUB46 and PUB48 gene loci precludes obtaining a double mutant by crossing the available single mutants. We thus applied microRNA technology to reduce the activity of all three gene products of the PUB46-48 subfamily by constructing an artificial microRNA (aMIR) targeted to this subfamily. Expressing aMIR46-48 in WT plants resulted in increased drought-sensitivity, a phenotype resembling that of the single pub46 and pub48 mutants, and enhanced sensitivity to methyl viologen, similar to that observed for the pub46 mutant. Furthermore, the WT plants expressing aMIR46-48 also revealed reduced inhibition by ABA at seed germination, a phenotype not evident in the single mutants. Expressing aMIR46-48 in pub46 and pub48 mutants further enhanced the drought sensitivity of each parental single mutant and of WT expressing aMIR46-48. Thus, whereas the gene-specific activity of the PUB46 and PUB48 E3s is partially redundant in that absence of either E3 leads 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.

Evolvability of Drought Response in Four Native and Non-native Conifers: Opportunities for Forest and Genetic Resource Management in Europe

Intraspecific genetic variation in drought response is expected to play an important role in determining the persistence of tree populations in global change as it (1) allows for spontaneous selection and local adaptation of tree populations, (2) supports assisted seed transfer of less-drought-sensitive provenance, and (3) enables the integration of drought-sensitivity traits into tree breeding. Estimating the potential of such adaptation options requires quantitative genetic knowledge of drought sensitivity across significant parts of species distributions and a comparative assessment of genetic variation within economically and ecologically important tree species. We quantified genetic variation within and among populations of four conifers growing within common garden experiments in the drought-prone eastern Austria. This region experienced three strong drought periods between 1980 and 2010 that resulted in significant reductions in radial growth. Among the four tested species, Douglas-fir revealed the highest resistance during drought and silver fir the best recovery after drought, while European larch and Norway spruce showed the lowest resistance. High genetic variation among populations and phenotypic stability across all three drought events was found for Norway spruce and silver fir, but not for the other species. Heritability and evolvability of drought traits, both approximated via genetic repeatability, revealed strong differences among populations of all four species. Repeatability and evolvability for resistance were highest in Norway spruce and, for recovery, highest in European larch. Our comparison indicates that the mean drought sensitivity of a species is not related to the intraspecific genetic variation in drought response. Thus, also highly drought-sensitive species, such as Norway spruce and European larch, harbor significant genetic variation in drought response within and among populations to justify targeted tree breeding, assisted gene flow, and supportive forest management to foster local adaptations to future conditions.