Autorregulação da biodisponibilidade do óxido nítrico em plantas: mecanismos moleculares e relação com o processo de assimilação de nitrato

Author(s)

Lucas Frungillo

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2015-07-23

Examining board members

Ione Salgado; Carlos Takeshi Hotta; Luciano Freschi; Celso Eduardo Benedetti; Rafael Vasconcelos Ribeiro

• Advisor: Ione Salgado

Abstract

This Thesis assesses the molecular mechanisms involved in the nitric oxide (NO)-mediated redox signalling, with a focus on the control of the nitrate assimilation process in the model plant Arabidopsis thaliana. To achieve the objectives of this Thesis, wild-type A. thaliana plants and cognates mutants were cultivated under nutrient controlled conditions and subjected to gene expression analysis by qPCR technique, determination of enzyme activities and metabolite content by spectrometry and fluorimetry, and metabolite fractionation by HPLC, as well as construction of transgenic lines of interest and analysis of protein post-translational modification. In Chapter I of this Thesis is presented a comprehensive scientific review published in the Brazilian Journal of Botany (DOI: 10.1007/s40415-013-0013-6) in which the established mechanisms of NO production, scavenging and signalling are detailed. In this chapter it is briefly described how the NO perception in biological systems has evolved, as well as a critical and comparative review of how NO homeostasis is achieved between plants and animals. Importantly, in Chapter I, the background technical and scientific information concerning the NO-mediated redox signalling that supports the experimental work presented in the following chapter is introduced. Chapter II presents a set of original experimental evidence indicating that in plants NO-mediated redox signalling impacts its own scavenging, through the enzymatic regulation of GSNOR1, and synthesis, through the nitrate assimilatory process. This chapter is organized as published in the scientific journal Nature Communications (DOI: 10.1038/ncomms6401). We provide evidence that S-nitrothiols feedback regulate nitrate uptake and reduction. Additionally, we present a robust set of evidence that GSNOR1 is directly inhibited by NO through S-nitrosylation. We conclude that a novel mechanism of NO self-control of bioavailability is involved in the fine-tuning of nitrate assimilation in plants. We then propose a model that summarizes our findings. Chapter III contains a manuscript submitted for publication as a book chapter in which a critical review is presented of recent advances in the NO signalling field, together with that of research on the nitrate assimilatory process. Especially, our recent findings are discussed in face of current knowledge, so this chapter can be read as an extension of the discussion presented in Chapter II. Along Chapter III, a detailed description of the nitrate assimilatory process and its intimate interplay with NO synthesis and scavenging in pants can be found. Throughout the text is highlighted what I consider promising objectives to the scientific progress in the field of plant nutrition, specially related with the redox signalling. As a scientific contribution of this Thesis, we propose a novel molecular mechanism of NO control of its own bioavailability with a significant impact on the nitrate assimilatory process in plants. I expect these new proposals to substantiate scientific research and agriculture practices aiming to raise crop yield and mitigate economic and environmental losses due to the excessive use of fertilizers (AU)

• FAPESP's process: 11/08931-8 - Role of the enzymes S-nitrosoglutathione reductase (GSNOR) and nitrate reductase (NR) in modulating the levels of nitric oxide (NO) in Arabidopsis thaliana
• Grantee: Lucas Frungillo Lima
• Support Opportunities: Scholarships in Brazil - Doctorate