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| Author(s): |
João Guilherme Portugal Vieira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia |
| Defense date: | 2019-11-06 |
| Examining board members: |
Michel Georges Albert Vincentz;
Jorge Mauricio Costa Mondego;
Celso Eduardo Benedetti;
Maria Helena de Souza Goldman;
Carlos Takeshi Hotta
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| Advisor: | Gustavo Turqueto Duarte; Michel Georges Albert Vincentz |
| Abstract | |
Phytohormones participate in various aspects of development and adjustment to stress conditions. Detection of a hormone by a receptor triggers a reprogramming of gene expression that characterizes the response to the hormone. Part of this response involves the activation of negative regulators, which promotes the attenuation of the hormonal signaling pathway, and thus, participating in the resetting of the system. The hormone abscisic acid (ABA) participates in some developmental processes and is crucial in triggering responses to abiotic stress conditions. The ABA core signaling pathway is composed of PYR/PYL/RCAR receptors, clade A PP2C phosphatases, and SnRK2 subclass III kinases. Increased ABA levels are perceived by PYR/PYL/RCAR receptors. The ABA and receptor complex sequester PP2C phosphatases, releasing SnRK2 kinases from the negative regulation by PP2Cs. Then, SnRK2 phosphorylates downstream proteins that are responsible for activating a gene expression program in response to the hormone. However, how the ABA signaling pathway is resetted is poorly elucidated. This work aims to unveil new aspects of the control of ABA signaling homeostasis. We showed that PYR/PYL/RCAR transcripts are continuously and robustly repressed by ABA, suggesting that negative feedback acts prominently on receptor expression. Moreover, transient ABA treatment revealed that recovery of initial receptor transcript levels is slow, indicating that control of receptor expression represents a limiting step in the resetting of the ABA signaling pathway. Genetic and pharmacological approaches suggest that SnRK2s are involved in the activation of mechanisms responsible for repression of receptor genes expression. Treatment with the transcriptional inhibitor (cordycepin) indicated that ABA promotes destabilization of PYL1/4/5/6 mRNA receptors. Genetic and molecular analyzes suggest that in the presence of ABA, miR5628, which is specific of Arabidopsis thaliana, promotes the cleavage of PYL6 transcript. In addition, we have shown that in the presence of the hormone, dcp5-1 and xrn4-5 mutants, which are deficient in decapping and exoribonuclease activity, respectively, show a greater amount of PYL6 transcripts than in wild type. Thus, we suggest that upon cleavage of the PYL6 mRNA, the RISC-3¿ fragment is degraded by XRN4, whereas the RISC-5¿ fragment is decapped, and then, degraded by XRN4. Decapping activity may also participate in the degradation process of PYL4 and PYL5 mRNAs in response to ABA, suggesting that decapping of the transcripts of PYL4/5/6 paralogues is an ancestral feature. Taken together, our data shed light on the importance of the control of ABA receptor expression in regulating ABA signaling homeostasis. Post-transcriptional regulation mechanisms contribute to attenuate ABA signaling by promoting the fast degradation of mRNA from a group of paralogous ABA receptors. Finally, we propose that miR5628 is an evolutionary novelty that was integrated in the negative feedback of the ABA core signaling pathway, increasing the degradation efficiency of PYL6 mRNA (AU) | |
| FAPESP's process: | 16/04897-3 - Evaluation of mRNA stability regulation of components of the Abscisic Acid (ABA) core signaling pathway |
| Grantee: | João Guilherme Portugal Vieira |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |