NRT2.2 is essential for nitrate uptake and carbon-nitrogen balance in Nannochloropsis oceanica

NITRATE TRANSPORTER 2.2 (NRT2.2) is the principal plasma-membrane nitrate transporter in Nannochloropsis oceanica, and its loss prevents nitrate uptake and growth recovery.

• Why it matters: Nitrate is a dominant nitrogen source for marine microalgae, but the uptake mechanisms that control how quickly cells resume growth after nitrate returns are unclear in key species.
• What they did: Using CRISPR knock-outs and confocal imaging, the study tested NRT2.2 versus its paralog NRT2.1 and tracked recovery after nitrogen starvation with nitrate resupply versus ammonium.
• The result: After nitrate resupply, nrt2.2 mutants failed to take up nitrate and did not resume growth, showing reduced photosystem II efficiency and chlorophyll and shifting fixed carbon into lipid and carbohydrate storage after 3 days.

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