The 2026 Nobel Prize in Physiology or Medicine has been awarded jointly to Karl Deisseroth, Peter Hegemann and Georg Nagel “for their discoveries concerning light-gated ion channels and optogenetics”. Optogenetics is a technique by which light-responsive ion channel proteins are used to manipulate the electrical properties of cells in living organisms. In neuroscience, this has proved nothing short of revolutionary, enabling researchers to stimulate or repress individual neurons, or small groups of neurons, at will. The technique is not only used to study the normal functioning of nervous systems but also their misfunctioning in conditions such as Parkinson’s disease; it even has potential therapeutic applications such as the partial restoration of sight in individuals with the degenerative eye disease retinitis pigmentosa. However, optogenetics has its roots not in the study of nerve cells, but in research on single-celled algae.

Peter Hegemann was initially curious about the light-seeking behaviour of Chlamydomonas reinhardtii. These relatively simple algae contain a single, cup-shaped chloroplast surrounding their nucleus, making them a good model to study the biophysics of photosynthesis. C. reinhardtii also has an ‘eyespot’ on its cell surface that contains the light-sensitive molecule retinal, and two flagella at its anterior end that either propel the alga in a straight line or make it tumble erratically depending on whether they are beating synchronously or asynchronously. The transitions between these two states are affected by light, with the result that the algae migrate towards any light source by active diffusion.

As early as 1991, Hegemann had shown that the behaviour of the flagella was controlled by electrical signals involving calcium ions dependent on retinal-binding proteins in C. reinhardtii’s eyespot. However, it wasn’t until the early 2000s that he and Georg Nagel identified two membrane proteins with sequence homology to the light-driven proton pump bacteriorhodopsin that is found in some Haloarchaea, which they named channelrhodopsin. Both bacteriorhodopsin and channelrhodopsin bind retinal, which changes conformation when it absorbs a photon of light. Bacteriorhodopsin uses the energy gained to pump protons across the cell membrane and power ATP synthesis. However, by expressing these proteins in Xenopus laevis oocytes and mammalian cell cultures, Hegemann and Nagel showed that the channelrhodopsins were light-activated pores, one permeable to protons (ChR1) and another to cations such as calcium or potassium (ChR2).

Karl Deisseroth was quick to see the potential for ChR2 as a light-activated switch to control the firing of nerve cells and thus explore the functioning of the brain and nervous system — an idea originally proposed by Francis Crick in a 1979 Scientific American essay. Working with Nagel, Deisseroth was able to express ChR2 in cultured nerve cells and control their activity with light on very short timescales. In little more than a year he had applied the approach to studying and manipulating the behaviour of live animals, establishing its utility for neuroscience research.

Although channelrhodopsins are proteins from the green lineage, the application of optogenetics to plant biology has lagged considerably behind its use in neuroscience owing to various technical problems. Channelrhodopsins need the co-factor retinal to function, but this is not produced by vascular plants. Also, plants have an abundance of photoreceptors responding to red light, and to blue and ultraviolet light, which complicates the interpretation of optogenetic effects. Retinal can be supplied exogenously, although this is not practical for whole-plant studies, and recently synthetic light-gated channels without the need for retinal have been created and used to control stomatal apertures or immune responses.

Perhaps the most promising solution to these problems is that developed by Nagel and collaborators. By using a channelrhodopsin from the cryptomonad alga Guillardia theta that responds to green light, wavelengths that are not absorbed by endogenous plant photoreceptors can be exploited. Also, the requirement for retinal can be achieved by engineering plants to produce the enzymes needed for its synthesis. This approach has been used to successfully investigate guard cells and stress responses.

The Nobel committee may not have had plants in mind when selecting the Prize in Physiology or Medicine this year. But by acknowledging a technique that arose from studies of green plants and that is actively applied to them, they may have awarded the closest thing to a Nobel for plant research since Barbara McClintock’s 43 years ago.

The story of channelrhodopsin is a reminder that model organisms chosen for their experimental convenience can yield tools of unexpected breadth. Chlamydomonas reinhardtii was never studied with neuroscience in mind; it was valued because its single cup-shaped chloroplast and tractable genetics made it a workhorse for photosynthesis research and flagellar biology. That the same organism’s eyespot would supply the molecular basis for a technique now deployed across neurobiology, cardiology and developmental biology illustrates how basic curiosity-driven research can produce dividends far beyond its original scope. The 2026 Nobel committee’s citation, framed entirely in the language of physiology and medicine, thus quietly honours a lineage of work rooted in phycology and plant-adjacent systems.

The biophysical logic underlying channelrhodopsins is worth unpacking. Retinal, a derivative of vitamin A, is the chromophore shared by the microbial rhodopsin family, which includes bacteriorhodopsin, halorhodopsin and the channelrhodopsins. When a photon is absorbed, retinal undergoes photoisomerization, switching from an all-trans to a 13-cis configuration. In bacteriorhodopsin, this conformational change drives a proton across the membrane against its gradient, storing energy that the cell can harvest as ATP. In channelrhodopsins, the same photochemical trigger instead opens a pore, allowing ions to flow down their electrochemical gradients. The distinction between a light-driven pump and a light-gated channel proved decisive: channels conduct ions passively and rapidly, which is precisely what is needed to depolarize a neuron on the millisecond timescales at which nerve cells operate.

The speed of adoption in neuroscience owed much to the fact that channelrhodopsin-2 could be expressed heterologously and gated by blue light, a wavelength that penetrates tissue reasonably well and is easy to deliver with conventional optics. Once the protein was shown to render cultured neurons light-sensitive, the conceptual barrier to controlling intact circuits fell almost immediately. Within a few years, optogenetics had been combined with fibre-optic delivery in behaving animals, allowing causal tests of the roles of specific cell types in behaviours ranging from sleep to reward seeking. The technique’s therapeutic promise, exemplified by trials using optogenetic proteins to confer light sensitivity on retinal cells in retinitis pigmentosa, represents a direct translation of algal photobiology into clinical medicine.

For plant scientists, the irony is palpable: the proteins are botanical in origin, yet plants themselves have been among the harder organisms to optogenetically engineer. The reasons are instructive. Vascular plants lack the enzymes to synthesize retinal, so any channelrhodopsin introduced into a plant genome remains non-functional unless the chromophore is supplied or the biosynthetic pathway is co-expressed. Moreover, plants are saturated with endogenous photoreceptors — phytochromes sensing red and far-red light, cryptochromes and phototropins sensing blue and ultraviolet-A — so any optogenetic stimulus delivered in those wavebands risks confounding the experiment with native light signalling. The green-light channelrhodopsin from Guillardia theta elegantly sidesteps the second problem, occupying a spectral window largely ignored by plant photoreceptors, while engineered retinal biosynthesis addresses the first. Together these advances have made it feasible to acutely manipulate ion fluxes in guard cells and to interrogate stress signalling pathways with a temporal precision that conventional genetics cannot match.

The comparison with Barbara McClintock is apt in more than sentiment. McClintock’s 1983 prize, awarded for her discovery of transposable elements in maize, recognized work done decades earlier in a plant system that much of the biomedical establishment had regarded as peripheral. Her mobile elements subsequently became foundational to genome biology across all kingdoms. Channelrhodopsins may follow a comparable arc: discovered in algae, elaborated in oocytes and cultured cells, industrialized in neuroscience, and now returning to the green lineage as tools for dissecting plant physiology. The 2026 prize is not formally a plant prize, but its intellectual genealogy runs directly through chloroplasts, eyespots and flagella — a fitting reminder that the boundaries between plant biology and medicine are thinner than award categories suggest.

Subject of Research: Nobels oblige

Article Title: Nobels oblige

Article References: Nobels oblige. (2026). Nature Plants. https://doi.org/10.1038/s41477-026-02455-w (Author names are not included in the publisher’s citation export.)

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02455-w

Keywords: Nobel Prize, optogenetics, channelrhodopsin, Chlamydomonas reinhardtii, neuroscience, plant biology, retinal, light-gated ion channels, Karl Deisseroth, Peter Hegemann, Georg Nagel, green lineage