The Myb-like transcription factor phosphorus starvation response (PtPSR) controls conditional P acquisition and remodelling in marine microalgae.

Amit Kumar Sharma,Juliette Jouhet,Atle M Bones,Ralph Kissen,Eric Maréchal,Per Winge,Alice Mühlroth,Leila Alipanah,Tore Brembu

doi:10.1111/nph.16248

Abstract

Phosphorus (P) is one of the limiting macronutrients for algal growth in marine environments. Microalgae have developed adaptation mechanisms to P limitation that involve remodelling of internal phosphate resources and accumulation of lipids. Here, we used in silico analyses to identify the P-stress regulator PtPSR (Phaeodactylum tricornutum phosphorus starvation response) in the diatom P. tricornutum. ptpsr mutant lines were generated using gene editing and characterised by various molecular, genetics and biochemical tools. PtPSR belongs to a clade of Myb transcription factors that are conserved in stramenopiles and distantly related to plant P-stress regulators. PtPSR bound specifically to a conserved cis-regulatory element found in the regulatory region of P-stress-induced genes. ptpsr knockout mutants showed reduction in cell growth under P limitation. P-stress responses were impaired in ptpsr mutants compared with wild-type, including reduced induction of P-stress response genes, near to complete loss of alkaline phosphatase activity and reduced phospholipid degradation. We conclude that PtPSR is a key transcription factor influencing P scavenging, phospholipid remodelling and cell growth in adaptation to P stress in diatoms.

Highlights

Phosphorus (P) is one of the most important macronutrients for algae and is a limiting factor of marine primary production in some parts of the world’s oceans (Sarthou et al, 2005; Elser et al, 2007)
When we investigated the transcriptional response to P limitation in genes encoding transcription factors (TFs) of the diatom P. tricornutum, using a publicly available dataset (Alipanah et al, 2018), the most responsive TF at 48 and 72 h after P deprivation was a transcript encoding a Myb-like TF annotated as PtMyb1R_SHAQKYF5 (Phatr2_47256), here re-named PtPSR
Two N. oceanica transcripts encoding Myb-like TFs closely related to PtPSR (No_10770 and No_8993 in the genome assembly by Vieler et al (2012)) displayed a similar early induction under P limitation, suggesting that the role of this TF is conserved among stramenopiles (Fig. S1)

Summary

Introduction

Phosphorus (P) is one of the most important macronutrients for algae and is a limiting factor of marine primary production in some parts of the world’s oceans (Sarthou et al, 2005; Elser et al, 2007) It can be found in its inorganic form (Pi, orthophosphate) or in dissolved organic phosphorus (DOP) (Van Mooy et al, 2009). Recent studies have revealed underlying common molecular mechanisms of stramenopiles to deal with P stress that can be divided into global and specific P-stress responses (Dyhrman et al, 2012; Cruz de Carvalho et al, 2016; Can~avate et al, 2017; Mu€hlroth et al, 2017; Alipanah et al, 2018). Even though a few molecular P-stress mechanisms are known, key transcriptional regulators have not been identified in stramenopiles

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Discussion

Conclusion