Circadian clock in photosynthetic eukaryotes (Archaeplastida) and stress adaptation

Author(s)

Cícero ALVES LIMA

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2018-04-06

Examining board members

Carlos Takeshi Hotta; Mariana Cabral de Oliveira; Estela Maria Plastino; Eduardo Moraes Rego Reis; João Carlos Setubal

• Advisor: Carlos Takeshi Hotta; Pio Colepicolo Neto

Abstract

Endogenous clocks control a large range of biological processes through biochemical oscillators that coordinate the signaling of environmental cues to metabolic pathways, allowing the perception of time and adjust to rhythmic changes. Cyclical daily behaviors were first noticed in plants and, more recently, revealed information about the transcriptional-translational feedback loops of genes that control these oscillators. Flowering is a well-known process where the perception of day length by the clock is intimately regulated by photoreceptors and by the central and peripheric genes of the biological clock. Multicellular organisms have a tissue-specific combination of expressed clock genes that may have different phase and period, increasing the complexity of this mechanism. Due to this reason, alternative models have been proposed for land plants-related photosynthetic eukaryotes. New models can simplify, for example, which combination of factors induce stress and how the biological clock is altered, allowing the anticipation of environmental changes and synchronization of physiology and environmental factors. This work aimed to verify how the biological clock adjusts to different kinds of stresses in 3 species: Gracilaria tenuistipitata (Rhodophyta), Ostreococcus tauri (Chlorophyta) and Saccharum sp (Embryophyta). Automated measurement techniques for growth rate and photosynthesis were stablished for the red alga. This alga also showed, after establishment of reference genes for RT-qPCRs normalization, an overexpression of TRX during the first hour under water deficit. In O. tauri, where the central clock genes are known, changes in LOV-HK and TOC1 gene expression are related to a higher growth rate under low and high temperatures, respectively. Besides, a specific combination of light, temperature and salinity can be an important trigger of seasonal blooms that causes important transcriptional changes at the central oscillator, what is similar to land plants. In Saccharum sp tolerant to drought, photosynthesis rhythms and CCA1 expression change their phase under simulated water deficit and drought responsive transcripts like HVA-22 and DRP are significantly up-regulated. In short, stress resets the clock in Saccharum sp, increasing the period of photosynthesis oscillation. In O.tauri, it induces a higher growth, keeping clock features. It was not possible to verify clock responses to stress in G.tenuistipitata, but methods to do so were stablished. The biological clock responses to stress can provide invaluable information for the better understanding about the growth and reproduction of organisms with a high biotechnological potential (AU)

• FAPESP's process: 13/05301-9 - Study on the interactions between the biological clock and desiccation in photosynthetic eukaryotes
• Grantee: Cícero Alves Lima Júnior
• Support Opportunities: Scholarships in Brazil - Doctorate