# Transcriptomic Responses of the Marine Diatom Phaeodactylum tricornutum to High Carbon and Low Nitrogen Stress

## TL;DR

This study explores how a marine diatom adjusts its gene activity to cope with high carbon and low nitrogen conditions, offering insights into its adaptability to changing ocean environments.

## Contribution

The study reveals the transcriptional mechanisms that allow diatoms to maintain carbon-nitrogen balance under combined high CO2 and low nitrogen stress.

## Key findings

- Key genes in carbon metabolism were upregulated, suggesting increased glycolytic and TCA cycle activity.
- Genes related to nitrogen assimilation were strongly induced under both high CO2 and low nitrogen conditions.
- Pathway analysis showed activation of lactic acid fermentation and nitrogen salvage pathways for energy conservation and nutrient recycling.

## Abstract

Diatoms play a pivotal role in global biogeochemical cycling and marine primary productivity, making them ideal model organisms for understanding how phytoplankton respond to environmental fluctuations associated with global climate change. In natural marine systems, diatoms frequently encounter simultaneous variations in carbon and nitrogen availability, yet most previous studies have examined the effects of these factors in isolation. To elucidate the integrated transcriptional mechanisms underlying diatom acclimation to coupled carbon–nitrogen (C—N) imbalance, we employed RNA sequencing (RNA‐Seq) to characterize the global transcriptional response of the model diatom
Phaeodactylum tricornutum
to high CO2 (~2000 μatm) and low nitrogen (10% of nitrogen concentration in f/2 medium) under parallel culture conditions. The results revealed both shared and distinct transcriptional responses between the two treatments. Key genes involved in carbon metabolism, such as phosphoglycerate mutase (PGAM_7) and dihydrolipoamide succinyltransferase (PHATRDRAFT_40430), were significantly upregulated, indicating enhanced glycolytic and TCA cycle activity. In contrast, the Calvin‐cycle enzyme fructose‐1,6‐bisphosphatase (FBPC4) was downregulated. Genes associated with nitrogen assimilation‐including nitrate reductase (PHATRDRAFT_54983), nitrite reductases (PHATRDRAFT_13154, PHATRDRAFT_8155), and ferredoxin–nitrite reductase (PHATRDRAFT_27757)‐were strongly induced under both conditions. Pathway enrichment analysis further indicated the activation of lactic acid fermentation and nitrogen salvage pathways, suggesting a metabolic shift toward energy conservation and nutrient recycling. Collectively, these findings provide an overview of the transcriptional adjustments that enable
P. tricornutum
to maintain C—N homeostasis under high CO2 and low nitrogen stress, offering new insights into diatom metabolic plasticity under changing ocean conditions.

To elucidate the integrated transcriptional mechanisms underlying diatom acclimation to coupled carbon–nitrogen (C—N) imbalance, we employed RNA sequencing (RNA‐Seq) to characterize the global transcriptional response of the model diatom
Phaeodactylum tricornutum
to high CO2 (~2000 μatm) and low nitrogen (10% of nitrogen concentration in f/2 medium) under parallel culture conditions. The results revealed both shared and distinct transcriptional responses between the two treatments. The findings provide an overview of the transcriptional adjustments that enable
P. tricornutum
to maintain C—N homeostasis under high CO2 and low nitrogen stress, offering new insights into diatom metabolic plasticity under changing ocean conditions.