Overexpression of PSR1 in Chlamydomonas reinhardtii induces luxury phosphorus uptake

Abstract

Remediation using micro-algae offers an attractive solution to environmental phosphate (Pi) pollution. However, for maximum efficiency, pre-conditioning of algae to induce luxury phosphorus (P) uptake is needed. Here we show that natural pre-conditioning can be mimicked through over-expression of a single gene, the global regulator PSR1 (Myb transcription factor: Phosphate Starvation Response 1), raising P levels to 8% dry cell weight from 2% in control. Complete removal of Pi occurred in log phase, unlike the control. This was associated with increases in PolyP granule size and uptake of Mg2+, the principal counterion. Hyper-accumulation of P depended on a feed-forward mechanism, where a small set of Class I genes were activated despite abundant external Pi levels. This drove a reduction in external Pi levels, permitting more genes to be expressed (Class II), leading to more Pi-uptake. These discoveries enable a bio-circular approach of recycling nutrients from wastewater back to agriculture. TeaserManipulating a single gene drove uptake of P and a Mg2+ counter-ion for increased PolyP accumulation.