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| Author(s): |
Nayara Patricia Vieira de Lira
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: | 2018-03-13 |
| Examining board members: |
Celso Eduardo Benedetti;
Cristina Elisa Alvarez Martinez;
Jörg Kobarg;
Luis Eduardo Soares Netto;
Silvana Aparecida Rocco
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| Advisor: | Celso Eduardo Benedetti |
| Abstract | |
Hydrogen sulfide (H2S) is well recognized as a toxic gas due to its capacity to strongly compete with oxygen for the cytochrome c oxidase (Cox), thus blocking aerobic respiration in many organisms. The bigR operon (Biofilm-Associated Growth Repressor), originally described in Xylella fastidiosa and Agrobacterium tumefaciens, and found conserved in related phytobacteria associated with soil and roots, plays a central role in H2S detoxification. The mechanism by which H2S is eliminated by the bigR operon involves the oxidation of the sulfur atom of H2S into sulfite. The bigR operon encodes the BigR repressor, the bifunctional Blh that shows sulfurtransferase (ST) and sulfurdioxygenase (SDO) activities, and a sulfite transporter. In a previous study, it was shown that the binging of BigR to its target DNA depends on the redox status of its two cysteines C42 e C108, which, when oxidized into an intrachain disulfide bond, changes the conformation of the helix-turn-helix domains of the repressor, disrupting its interaction with DNA, thus activating the operon. However, the nature of the signaling molecule responsible for BigR oxidation remained elusive for many years. In addition, in previous genetic studies, it was found that the Blh protein was necessary for H2S oxidation and required for bacterial growth under hypoxia. Nevertheless, the biochemical mechanism by which Blh promotes such phenotypes was not known. Here, we show that H2S was capable of inducing the disulfide bond formation between C42 and C108 inactivating the repressor and activating do operon. Moreover, we show that enzymatic activities displayed by the ST e SDO domains of Blh are coupled and dependent of reduced glutathione, and that these activities are essential to maintain aerobic respiration under hypoxia. We also found that both the ST e SDO reactions produce sulfite as a product. Thus, knowing that sulfite is toxic to plants, we investigated a possible effect of sulfite toxicity in citrus infected with X. fastidiosa showing typical Citrus Chlorosis Variegated (CVC) symptoms. We found that sulfite causes chlorosis in citrus leaves and that sweet orange plants infected with X. fastidiosa showed higher sulfite contents and higher levels of transcripts for the SiR (Sulfite reductase) and SO (sulfite oxidase) genes, which are involved in sulfite detoxification in plants. Our data thus suggest that plants infected with X. fastidiosa are under sulfite stress and that sulfite that is produced as a result of the activity of the bigR operon might contribute to the development of CVC symptoms (AU) | |
| FAPESP's process: | 13/24043-0 - Functional analysis of the bigR operon from Xylella fastidiosa: identification of inhibitor molecules for the sulfur dioxygenase Blh and possible redox mechanism involved in BigR oxidation and operon activatio |
| Grantee: | Nayara Patricia Vieira de Lira |
| Support Opportunities: | Scholarships in Brazil - Doctorate |