Integrative analysis of proteomics, metabolomics and lipidomics to study the accumulation of neutral lipids in the microalgae Chlamydomonas reinhardtii

Author(s)

Laís Albuquerque Giraldi

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2021-08-06

Examining board members

Flavia Vischi Winck; Rafael Silva Rocha

• Advisor: Flavia Vischi Winck

Abstract

As microalgae have a rich chemical composition, with a high content of oils, proteins, carbohydrates, pigments, minerals and vitamins, they have a high potential as raw material for sustainable production in various commercial sectors such as biofuels, pharmaceuticals, agriculture, food and pigments. Due to the greenhouse gas emissions reduction goes and the high capacity to accumulate neutral lipids, microalgae have gained interest by the bioenergy sector in the last decade, in order to produce biodiesel. However, in general, high neutral lipid concentrations and high biomass productivity are inversely correlated, therefore, genetic and bioprocess improvements are needed to make the microalgal biomass usage viable and commercially competitive. The environmental condition that most contributes to an increase in neutral lipids, such as triacylglycerols (TAGs), is the nitrogen (N) starvation. In this condition, cells are induced into a cell quiescence phase which cell divisions are stopped and TAGs levels increase inside the cells. In addition to cultivation optimization studies, previous studies also used the strategy of gene overexpression and inactivation involved in TAGs and starch biosynthesis aiming to increase the TAGs production in the cells. However, these studies demonstrated that optimization strategies are still expensive and, the alteration of one or a few genes did not lead to the expected TAG productivity in a sustainable way. Given this scenario, a systems biology approach using \"omics\" data is essential to generate information and understand the mechanisms involved with the accumulation of TAGs in microalgae. Therefore, the aim of the study was to investigate, through an omics data integrative approach, the accumulation of TAGs in response to N starvation in photoautotrophic condition in Chlamydomonas reinhardtii. Time series experiments (with 10 time points) were performed to detect alterations in the proteome, metabolome and lipidome. Furthermore, the nuclear proteome was investigated looking for regulatory proteins. Through the systematic and integrative analysis of the \"omics\" data, together with the physiological observations, it was found that, under the conditions tested, the TAGs accumulation is a result of several pathways regulation together. The metabolic pathways of gluconeogenesis, ATP generation process, light reaction in photosynthesis and Arg biosynthetic process were shown to be central in the response to N starvation. Furthermore, it was found that, under the tested conditions, the higher contribution to TAGs accumulation was probably membrane lipid remodeling. The nuclear proteome results revealed that a transcription factor protein (Tubby-like protein) may be a negative regulator of cell proliferation. In addition, based on the meta-analysis performed using trascriptomes data from other studies, it was suggested that the alteration in the Arg pathway apparently is not exclusive of the N starvation response, being also upregulated under other types of stress. Therefore, we could conclude that the objectives of the present study were achieved, and its findings expanded the current knowledge about the molecular mechanisms that lead to the accumulation of TAGs in C. reinhardtii under photoautotrophic condition. (AU)

• FAPESP's process: 16/19152-3 - Identification of regulatory networks related to lipid accumulation in the microalgae Chlamydomonas reinhardtii
• Grantee: Lais Albuquerque Giraldi
• Support Opportunities: Scholarships in Brazil - Doctorate