Die Rolle des Glutaredoxins ROXY21 beim programmierten Zelltod
Final Report Abstract
Mitochondria have long been recognized to be associated with PCD in both plants and animals, and their dysfunction has been shown to correlate with cell and organismal aging in yeast, invertebrates, and mammals. Seemingly paradox, the reduction of mitochondria function can also extend lifespan as shown for Caenorhabditis and Drosophila. Previous work from our lab has extended the current view of mitochondria associated cell death regulation as we were able to show that mitochondria dysfunction can affect cellular lifespan in a non-cell autonomous manner. The aim of this study was to characterize the eda39 mutant defective in antipodal cell degeneration on a morphological, molecular and functional level. According to the annotation and our preliminary results, the T-DNA mutation in eda39 interrupted the ROXY21 gene and we thus also aimed to analyze the role of ROXY21 for non-cell autonomous antipodal cell degeneration and plant senescence. Mutant analysis revealed that eda39 is defective in polar nuclear fusion of the central cell and antipodal degeneration, reminiscent to the previously characterized syco-1 mutant. The defect is associated with a substantial disintegration of the internal mitochondrial membrane system and reduced fertility, while molecular marker analysis suggested that the overall cell specification pattern was not affected. Notably, a genomic ROXY21 fragment did not complement the mutant and an independent mutant allele exhibited no female gametophytic defect. We therefore performed whole genome sequencing to find out that roxy21-2 is part of a substantial genome deletion comprising 27 genes. Among the deleted loci in the eda39 mutant is AT4g32915, which codes for the glutamyl-tRNA aminotransferase subunit C (GatC). Because of the close resemblance between eda39/+ and syco-1/+ and the similarity between their protein functions, we hypothesized that loss of GatC in eda39/+ mutants causes the phenotype. We could show that the gene is expressed in the central cell of the female gametophyte and that a genomic GatC copy, indeed, almost fully complemented the eda39 mutant defect. Intriguingly, we could show that two further randomly chosen aminoacetyl-tRNA synthetases are expressed in the central cell but not other female gametophytic cells, suggesting that the central cell acts as a metabolic center. We went one step further and asked how changes of mitochondrial activity are translated into cellular longevity cues. In order to analyze the role of reactive oxygen species we characterized the expression of H2O2 scavenging catalases in the female gametophyte. Together with cell-type specific overexpression and RNAi experiments our results suggest that ROS is an important signaling cue for the regulation of polar nuclear fusion and antipodal cell degeneration. Our data were further substantiated by cell-type specific modulation of selected glutaredoxins involved in redox homeostasis. Finally, we addressed the role of the heat transcription factor HsfA2, which is considered a redox sensor and which we found to be expressed in antipodal cells. We generated a dominant negative hsfa2 allele by deleting the nuclear export sequence and showed that this approach interferes with antipodal cell degeneration. Together, our data suggest that the central cell operates as the metabolic center of the female gametophyte and that its mitochondrial activity is reflected by the ROS status within that cells. This information is communicated to adjacent antipodal cells, where the signal is translated in an Hsfa2-dependent manner to mediate cell death.
Publications
- (2017). Molecular movement in the Arabidopsis thaliana female gametophyte. Plant Reprod 30:141
Erdmann RM, Hoffmann A, Walter HK, Wagenknecht HA, Groß-Hardt R, Gehring M
(See online at https://doi.org/10.1007/s00497-017-0304-3) - (2017). Patterning the female gametophyte of flowering plants. Plant Physiol 173:122
Tekleyohans DG, Nakel T, Groß-Hardt R
(See online at https://doi.org/10.1104/pp.16.01472)
