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

Abstract

Summary 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.

Mobilization and Cellular Distribution of Phosphate in the Diatom Phaeodactylum tricornutum

“…These data, although generated by different experimental designs (e.g., duration of P i starvation) or diatom species, indicated a global transcriptomic reprogramming, which should influence the protein composition of many cell compartments, accompanied by several physiological responses. In addition, a Myb-like transcription factor, P starvation response (PtPSR), which controls cellular adaptations to P i stress, has recently been identified in Phaeodactylum tricornutum (Sharma et al, 2019). The response to P i limitation correlates with a specific transcriptional upregulation of genes coding for alkaline phosphatases that are necessary for phosphate acquisition from DOP.…”

A novel Ca2+signalling pathway co-ordinates environmental phosphorus sensing and nitrogen metabolism in marine diatoms

“…However, we did find four Ca 2+ sensor-kinase genes upregulated during phosphorus limitation. Notably, they also contain recognition motifs for the phosphorus-stress Myb-like transcriptional regulator PtPSR (Sharma et al, 2019). Our work thus paves the way to future advances in our understanding of the genetic components, evolutionary distribution, and broader roles of phosphate-Ca 2+ signalling in controlling phosphorus-stress recovery in diatoms, and potentially eukaryotes more broadly.…”

“…Diatoms, and other phytoplankton, also substitute phospholipids with non-phosphorus forms to decrease cellular demand (Martin et al, 2011; Van Mooy et al, 2009). A transcriptional regulator, distantly related to phosphate starvation regulator protein (PSR1) of Chlamydomonas (Wykoff et al, 1999), was recently found to coordinate such metabolic adaptations in diatoms (Sharma et al, 2019). However, these studies primarily focus on mechanisms underpinning phosphorus limitation responses.…”

Potential and Challenges of Improving Photosynthesis in Algae

“…In N. gaditana, 20 putative regulators of lipid production, down-regulated by nitrogen deprivation, were identified by RNA-seq; a strategy of selective knock-out by the Crispr-Cas9 system allowed us to identify a homolog of the fungal Zn(II) 2 Cys 6 -encoding gene, which triggered lipid biosynthesis in Nannochloropsis and resulted in a 200% increase of C partition to lipids, without significantly affecting the growth rate [152]. More recently, a Myb-like transcription factor Phosphorus Starvation Response (PtPSR) was identified in P. tricornutum; its modulation might represent a good strategy to enhance cell growth and TAG production in limited-phosphorous conditions [153]. A MYB DNA binding protein involved in cell cycle regulation was instead targeted in Chlamydomonas, showing that the mutants devoid of CrCDC5 accumulate more oil and starch with respect to WT [154].…”