Abstract
BackgroundPlants respond to abiotic stress on physiological, biochemical and molecular levels. This includes a global change in their cellular proteome achieved by changes in the pattern of their protein synthesis and degradation. The ubiquitin-proteasome system (UPS) is a key player in protein degradation in eukaryotes. Proteins are marked for degradation by the proteasome by coupling short chains of ubiquitin polypeptides in a three-step pathway. The last and regulatory stage is catalyzed by a member of a large family of substrate-specific ubiquitin ligases.ResultsWe have identified AtPUB46 and AtPUB48—two paralogous genes that encode ubiquitin ligases (E3s)—to have a role in the plant environmental response. The AtPUB46, −47, and −48 appear as tandem gene copies on chromosome 5, and we present a phylogenetic analysis that traces their evolution from an ancestral PUB-ARM gene. Single homozygous T-DNA insertion mutants of AtPUB46 and AtPUB48 displayed hypersensitivity to water stress; this was not observed for similar mutants of AtPUB47. Although the three genes show a similar spatial expression pattern, the steady state levels of their transcripts are differentially affected by abiotic stresses and plant hormones.ConclusionsAtPUB46 and AtPUB48 encode plant U-Box E3s and are involved in the response to water stress. Our data suggest that despite encoding highly homologous proteins, AtPUB46 and AtPUB48 biological activity does not fully overlap.
Highlights
Plants respond to abiotic stress on physiological, biochemical and molecular levels
Proteins are targeted for degradation by the 26S proteasome by covalent attachment of a short chain of ubiquitin molecules [5] performed by a sequence of three enzymes, a ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), and a ubiquitin ligase (E3) that recognizes the substrate [7]
Gene organization of At5G18320, At5G18330 and At5G18340 and domain organization of the AtPUB46, AtPUB47 and AtPUB48 proteins they encode We screened Arabidopsis E3 T-DNA insertion mutants for altered tolerance to water stress and found a homozygous T-DNA insertion mutant of AtPUB46 with enhanced sensitivity to water stress. This gene is a member of a cluster of 3 loci (At5G18320, At5G18330 and At5G18340) on the upper arm of chromosome 5 that encode highly homologous U-box protein ligases (AtPUB46 to AtPUB48, respectively, Fig. 1a)
Summary
Plants respond to abiotic stress on physiological, biochemical and molecular levels This includes a global change in their cellular proteome achieved by changes in the pattern of their protein synthesis and degradation. Plants respond to abiotic stress with major physiological, biochemical and molecular changes that lead to a new homeostasis These changes include a global alteration of the plant transcriptome, proteome, and metabolome that result from a new balance between the rates of cellular biosynthesis and degradation activities. Proteins are targeted for degradation by the 26S proteasome by covalent attachment of a short chain of ubiquitin molecules [5] performed by a sequence of three enzymes, a ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), and a ubiquitin ligase (E3) that recognizes the substrate [7]. Protein ubiquitylation is mostly associated with degradation, ubiquitylation plays a role in signaling and modification of protein activities [6] giving the E3s a critical role in cell function
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