Regulation of plant stress responses by clade I TGA transcription factors and interacting CC-type glutaredoxins
von Anja Maren Pelizaeus
Datum der mündl. Prüfung:2023-03-30
Erschienen:2023-11-09
Betreuer:Prof. Dr. Christiane Gatz
Gutachter:Prof. Dr. Christiane Gatz
Gutachter:Prof. Dr. Marcel Wiermer
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http://dx.doi.org/10.53846/goediss-10180
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Name:Dissertation Anja Maren Pelizaeus.pdf
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Zusammenfassung
Englisch
TGACG-BINDING (TGA) transcription factors are important regulators in numerous processes such as pathogen defense, development and detoxification. To control some of these responses, plant specific CC type glutaredoxins (ROXYs) interact with and repress TGA factors. The Arabidopsis thaliana genome encodes 21 ROXYs, which can be further divided according to their C terminus. 17 members encode an ALWL motif whereas four ROXYs do not contain this motif. ROXYs can recruit the transcriptional co-repressor TOPLESS (TPL) through the ALWL motif. TPL-mediated repression represents most likely one of the mechanisms of how ROXYs control the activity of TGAs. ROXY6, 7, 8 and 9 are the only ROXYs without an ALWL motif. Analysis of plants ectopically expressing ROXY8 or ROXY9 has shown that they repress the activity of clade I TGAs (TGA1, TGA4), but not the activity of clade II TGAs (TGA2, TGA5, TGA6). In this thesis, we wanted to analyze how gene expression is regulated by ROXY6, 7, 8, 9. Previous studies showed that the expression of ROXY6, ROXY8 and ROXY9 is induced in the shoots upon nitrogen (N) starvation. Subsequently, the ROXYs travel to the roots, where they activate expression of genes for e.g. nitrate uptake. As TGA1 and 4 are also involved in N starvation responses, ROXY6, 7, 8, 9 and TGA1, 4 might regulate the expression together. Using transcriptome analysis, we identified 350 genes that are activated by ROXY6, 7, 8, 9 under N limiting conditions as well as 212 repressed genes. We found that TGA1, 4 can function as a repressor of those genes that are induced upon N starvation and that ROXY6, 7, 8, 9 serve to interfere with this repression. Proximity labeling experiments identified TPL as an indirect interaction partner. Since ROXY9 interacts with proteins of the JASMONATE ZIM DOMAIN (JAZ) family and since JAZs interact with TPL through the adaptor protein NOVEL INTERACTOR OF JAZ (NINJA), analysis of the corresponding loss-of-function mutants was performed. These studies suggest that the repressive capacity of ROXY6, 7, 8, 9 is dampened by the JAZ/NINJA/TPL complex. As JA signaling leads to the degradation of JAZ, enhanced JA levels might further promote activation of gene expression. To further determine the mechanism of ROXY9-mediated gene expression, the importance of the CCLC active site motif was analyzed. The active center of a glutaredoxin is required for oxidoreductase activities or binding of iron sulfur (Fe-S) clusters. Surprisingly, the first and second cysteine of the active site motif are dispensable, indicating that oxidoreductase activity or Fe-S cluster binding is not involved in the regulation. Besides their function in the regulation of N starvation responses, TGA1, 4 are involved in activation of gene expression to induce systemic acquired resistance (SAR). SAR is established in uninfected leaves upon local pathogen infection. When a SAR leaf is attacked by a pathogen, it mounts a much more effective defense response compared to the naïve leaf. For the establishment of SAR, the plant hormones salicylic acid (SA) and N-hydroxypipecolic acid (NHP) are synthesized. Inductionof SA and NHP synthesis genes requires basal SA levels, while other SAR genes, like PR1, require pathogen-induced SA levels for maximum induction. In this study, we wanted to analyze in how far the response to Psm-infected SAR leaves depends on the two different TGA clades at basal SA levels. For this, we performed transcriptome analysis with the respective mutants in the sid2 background in Psm-infected SAR leaves. 4184 induced genes were identified of which most are regulated to some extent by one or both TGA clades. WRKY51 and its closest homologue WRKY50 are activated only by TGA1, 4 in SAR conditions. Together with TGA2, 5, 6, WRKY50, 51 might regulate the expression of SAR-induced genes. No transcription factor was highly induced by only clade II TGAs, suggesting that most TGA2, 5, 6-induced factors are also activated by clade I TGAs. For example, WRKY75 and WRKY31 are highly upregulated in SAR by both TGA clades. They could amplify the response and activate even promoters without TGA binding sites.
Keywords: TGA transcription factors; CC-type glutaredoxins; nitrogen starvation; TurboID; systemic acquired resistance; hyponastic growth
