A bona fide La protein is required for embryogenesis in Arabidopsis thaliana

Searches in the Arabidopsis thaliana genome using the La motif as query revealed the presence of eight La or La-like proteins. Using structural and phylogenetic criteria, we identified two putative genuine La proteins (At32 and At79) and showed that both are expressed throughout plant development but at different levels and under different regulatory conditions. At32, but not At79, restores Saccharomyces cerevisiae La nuclear functions in non-coding RNAs biogenesis and is able to bind to plant 3′-UUU-OH RNAs. We conclude that these La nuclear functions are conserved in Arabidopsis and supported by At32, which we renamed as AtLa1. Consistently, AtLa1 is predominantly localized to the plant nucleoplasm and was also detected in the nucleolar cavity. The inactivation of AtLa1 in Arabidopsis leads to an embryonic-lethal phenotype with deficient embryos arrested at early globular stage of development. In addition, mutant embryonic cells display a nucleolar hypertrophy suggesting that AtLa1 is required for normal ribosome biogenesis. The identification of two distantly related proteins with all structural characteristics of genuine La proteins suggests that these factors evolved to a certain level of specialization in plants. This unprecedented situation provides a unique opportunity to dissect the very different aspects of this crucial cellular activity

AtCXXS: atypical members of the Arabidopsis thaliana thioredoxin h family with a remarkably high disulfide isomerase activity

International audienc

Complementation of Seed Maturation Phenotypes by Ectopic Expression of ABSCISIC ACID INSENSITIVE3, FUSCA3 and LEAFY COTYLEDON2 in Arabidopsis

International audienceABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3) and LEAFY COTYLEDON2 (LEC2), collectively the AFL, are master regulators of seed maturation processes. This study examined the role of AFL in the production of seed reserves in Arabidopsis. Quantification of seed reserves and cytological observations of afl mutant embryos show that protein and lipid but not starch reserves are spatially regulated by AFL. Although AFL contribute to a common regulation of reserves, ABI3 exerts a quantitatively greater control over storage protein content whereas FUS3 controls lipid content to a greater extent. Although ABI3 controls the reserve content throughout the embryo, LEC2 and FUS3 regulate reserves in distinct embryonic territories. By analyzing the ability of an individual ectopically expressed AFL to suppress afl phenotypes genetically, we show that conserved domains common to each component of the AFL are sufficient for the initiation of storage product synthesis and the establishment of embryo morphology. This confirms redundancy among the AFL and indicates a threshold necessary for function within the AFL pool. Since no individual AFL was able to suppress the tolerance to desiccation, mid- and late-maturation programs were uncoupled

A network of local and redundant gene regulation governs Arabidopsis seed maturation

In Arabidopsis thaliana, four major regulators (ABSCISIC ACID INSENSITIVE3 [ABI3], FUSCA3 [FUS3], LEAFY COTYLEDON1 [LEC1], and LEC2) control most aspects of seed maturation, such as accumulation of storage compounds, cotyledon identity, acquisition of desiccation tolerance, and dormancy. The molecular basis for complex genetic interactions among these regulators is poorly understood. By analyzing ABI3 and FUS3 expression in various single, double, and triple maturation mutants, we have identified multiple regulatory links among all four genes. We found that one of the major roles of LEC2 was to upregulate FUS3 and ABI3. The lec2 mutation is responsible for a dramatic decrease in ABI3 and FUS3 expression, and most lec2 phenotypes can be rescued by ABI3 or FUS3 constitutive expression. In addition, ABI3 and FUS3 positively regulate themselves and each other, thereby forming feedback loops essential for their sustained and uniform expression in the embryo. Finally, LEC1 also positively regulates ABI3 and FUS3 in the cotyledons. Most of the genetic controls discovered were found to be local and redundant, explaining why they had previously been overlooked. This works establishes a genetic framework for seed maturation, organizing the key regulators of this process into a hierarchical network. In addition, it offers a molecular explanation for the puzzling variable features of lec2 mutant embryos

Interplay between the NADP-Linked Thioredoxin and Glutathione Systems in Arabidopsis Auxin Signaling[C][W]

NADP-linked thioredoxin and glutathione systems are key reduction pathways in living organisms. Based on a genetic approach, this study shows that these pathways interfere with auxin transport and metabolism, defining a link between redox regulation and auxin signaling

Arabidopsis glutaredoxin S17 and its partner NF-YC11/NC2α contribute to maintenance of the shoot apical meristem under long-day photoperiod

International audienceGlutaredoxins (GRXs) catalyze the reduction of protein disulfide bonds using glutathione as a reductant. Certain GRXs are able to transfer iron-sulfur clusters to other proteins. To investigate the function of Arabidopsis (Arabidopsis thaliana) GRXS17, we applied a strategy combining biochemical, genetic, and physiological approaches. GRXS17 was localized in the nucleus and cytosol, and its expression was elevated in the shoot meristems and reproductive tissues. Recombinant GRXS17 bound Fe2S2 clusters, a property likely contributing to its ability to complement the defects of a Baker's yeast (Saccharomyces cerevisiae) strain lacking the mitochondrial GRX5. However, a grxs17 knockout Arabidopsis mutant exhibited only a minor decrease in the activities of iron-sulfur enzymes, suggesting that its primary function is as a disulfide oxidoreductase. The grxS17 plants were sensitive to high temperatures and long-day photoperiods, resulting in elongated leaves, compromised shoot apical meristem, and delayed bolting. Both environmental conditions applied simultaneously led to a growth arrest. Using affinity chromatography and split-Yellow Fluorescent Protein methods, a nuclear transcriptional regulator, the Nuclear Factor Y Subunit C11/Negative Cofactor 2α (NF-YC11/NC2α), was identified as a GRXS17 interacting partner. A mutant deficient in NF-YC11/NC2α exhibited similar phenotypes to grxs17 in response to photoperiod. Therefore, we propose that GRXS17 interacts with NF-YC11/NC2α to relay a redox signal generated by the photoperiod to maintain meristem function