Nitrogen-induced metabolic changes and molecular determinants of carbon allocation in Dunaliella tertiolecta.

Kenneth Wei Min Tan,Hui Shen,Huixin Lin,Yuan Kun Lee

doi:10.1038/srep37235

Kenneth Wei Min Tan, Hui Shen + Show 2 more

Open Access

https://doi.org/10.1038/srep37235

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Journal: Scientific Reports	Publication Date: Nov 16, 2016
Citations: 56	License type: CC BY 4.0

Affiliation: National University of Singapore

Abstract

Certain species of microalgae are natural accumulators of lipids, while others are more inclined to store starch. However, what governs the preference to store lipids or starch is not well understood. In this study, the microalga Dunaliella tertiolecta was used as a model to study the global gene expression profile regulating starch accumulation in microalgae. D. tertiolecta, when depleted of nitrogen, produced only 1% of dry cell weight (DCW) in neutral lipids, while starch was rapidly accumulated up to 46% DCW. The increased in starch content was accompanied by a coordinated overexpression of genes shunting carbon towards starch synthesis, a response not seen in the oleaginous microalgae Nannochloropsis oceanica, Chlamydomonas reinhardtii or Chlorella vulgaris. Genes in the central carbon metabolism pathways, particularly those of the tricarboxylic acid cycle, were also simultaneously upregulated, indicating a robust interchange of carbon skeletons for anabolic and catabolic processes. In contrast, fatty acid and triacylglycerol synthesis genes were downregulated or unchanged, suggesting that lipids are not a preferred form of storage in these cells. This study reveals the transcriptomic influence behind storage reserve allocation in D. tertiolecta and provides valuable insights into the possible manipulation of genes for engineering microorganisms to synthesize products of interest.

Highlights

It is a robust species that is able to maintain high growth rates in a wide range of pH, temperature and light, and contain relatively high lipid content[2,24,25]
Our investigations into the transcriptome profile via RNA-seq uncovered key characteristics linked to increased activity in the central carbon metabolism (CCM) pathways such as the tricarboxylic acid (TCA) cycle, glycolysis and the oxidative pentose phosphate pathway (OPPP) that may contribute to carbon flux and starch synthesis
D. tertiolecta strain University of Texas at Austin (UTEX) LB 999 was grown in ATCC1174 DA medium with an initial nitrate concentration of 5 mM and 0.5 mM for N-replete and N-deplete cultures respectively

Summary

Introduction

It is a robust species that is able to maintain high growth rates in a wide range of pH, temperature and light, and contain relatively high lipid content[2,24,25]. Shin et al independently annotated the transcriptome of D. tertiolecta and studied possible genes related to growth limitation during N-depletion[29]. We aim to determine the underlying changes in gene expression which may influence storage product accumulation in D. tertiolecta, and establish a transcriptomic basis for the preference of D. tertiolecta to store one product over another. We tracked for dynamic changes of storage components including starch, glycerol, neutral lipids and total fatty acids, and compared the transcriptome profile of the cell in the exponential and stationary phases after nitrogen has been depleted in the media. We compared our findings with microalgae species of varying oleaginicity to better understand the underlying differences that determine the preferred production of starch and/or lipids

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