Thylakoids reorganization enables driving photosynthesis under far-red light in the microalga Nannochloropsis gaditana

Oxygenic photosynthesis is driven by visible light in most photosynthetic organisms, with exceptions in few cyanobacteria and microalgae species, that can extend the light absorption to far-red wavelengths, by synthesizing new pigments or shifting the antennae absorption range beyond 700 nm.

In this work, we describe a novel mechanism of acclimation in the marine microalga Nannochloropsis gaditana , that resulted capable of growth relying solely on far-red light. Unexpectedly, the response did not involve the synthesis of red-shifted absorption forms, rather a peculiar reorganization of chloroplasts.

The abundance of photosynthetic complexes changed, with an increased accumulation of all pigment binding proteins and photosystem II. Chloroplasts became bigger and thylakoid membranes increased in number occupying almost all the organelle volume, showing also newly observed structures, composed of a central superstack with perpendicular electrondense interconnections, that we propose to name thylakoidal bodies .

To the best of our knowledge, these results describe a novel acclimation strategy to far-red light, overall highlighting that the biodiversity of responses to far-red light is currently underestimated.