A familiar plant enzyme may help send damaged mitochondria for recycling

An unexpected recycling role

Mitochondria are central to cellular energy metabolism, but damaged or excess mitochondria must also be removed. One route is mitophagy: a selective recycling process in which mitochondria are enclosed by membrane structures called autophagosomes and delivered to the vacuole for breakdown.

A bioRxiv preprint posted on November 2, 2026, proposes an unexpected participant in this process in Arabidopsis thaliana. Huifang Lin and colleagues report that GSNOR1, an enzyme best known for breaking down S-nitrosoglutathione, may also act as a receptor that helps connect damaged mitochondria to the recycling machinery. The work has not been certified by peer review.

Their model centers on three proteins: GSNOR1, VDAC3 on the mitochondrial outer membrane, and ATG8, a protein involved in autophagy. The authors propose that their interactions help recruit an enclosing membrane around damaged mitochondria.

What happens without GSNOR1?

The researchers first examined plants with a loss-of-function mutation in GSNOR1. These plants had higher levels of mitochondrial DNA and several mitochondrial marker proteins than unmodified plants, findings the authors interpret as evidence of mitochondrial accumulation.

Electron microscopy also revealed structural defects. In the root sections examined, about 22% of mitochondria in the GSNOR1 mutant had abnormal internal folds, called cristae, compared with about 1.5% in unmodified plants. Fluorescent imaging further indicated that many mutant mitochondria had lost their normal membrane potential—the electrochemical difference across the inner membrane.

To challenge the system, the team used 2,4-dinitrophenol, or DNP, which disrupts that potential. In unmodified plants, DNP reduced the abundance of mitochondrial marker proteins. That reduction was impaired in GSNOR1 mutants, consistent with less effective removal of damaged mitochondria. Electron microscopy also showed damaged mitochondria that were not enclosed by autophagosomes in the mutants.

The authors additionally tracked the breakdown of fluorescently tagged mitochondrial proteins. They describe changes consistent with impaired mitophagy, although the figure legend labels the quantified comparisons for one of these assays as not statistically significant. That result should therefore be read alongside the other evidence, rather than as decisive proof by itself.

Connecting mitochondria to the disposal machinery

Under normal conditions, fluorescently tagged GSNOR1 was distributed mainly through the cytosol, the fluid compartment outside organelles. After DNP treatment, it increasingly appeared alongside mitochondria. The researchers interpret this movement as recruitment to mitochondria that have lost membrane potential.

Protein-binding experiments showed interactions between GSNOR1 and ATG8. GSNOR1 contains two short sequence features known as ATG8-interacting motifs, and substitutions in these motifs reduced binding in laboratory assays.

A search for mitochondrial partners also identified VDAC proteins. Several experiments supported their interaction with GSNOR1, with VDAC3 showing the strongest binding in a purified-protein assay. VDAC3 could also bind ATG8 directly. Deletion experiments implicated the first 34 amino acids of VDAC3 as important for binding both partners.

Together, these findings support the authors’ proposal that GSNOR1 and VDAC3 cooperate in linking mitochondria to ATG8-associated membranes. The three fluorescently tagged proteins also appeared together in small cellular spots, consistent with their proposed partnership.

Stress responses and unresolved questions

Plants lacking GSNOR1 were more sensitive to prolonged DNP exposure, while both GSNOR1 and VDAC3 mutants showed poorer root-growth recovery after a shorter treatment. VDAC3 mutants also contained mitochondria with damaged cristae. These observations connect the proposed mechanism to the plants’ ability to cope with experimentally induced mitochondrial stress.

The effect was not universal across the conditions tested. GSNOR1 mutants showed no apparent difference from unmodified plants in the reported starvation assays, limiting conclusions about its role across different triggers of mitochondrial recycling.

There are also unresolved mechanistic details. A GSNOR1 variant altered in both ATG8-interacting motifs failed to restore normal development, but it accumulated at lower levels. The authors acknowledge that instability, and possibly altered enzyme activity, complicates interpretation of that experiment.

Genetic comparisons suggested that excess nitric oxide signaling alone did not explain the mitochondrial defects under the tested conditions. However, the authors do not exclude an additional contribution from GSNOR1’s established enzymatic role.

The central proposal is therefore a second job for a familiar enzyme: helping select damaged mitochondria for recycling. Whether the same arrangement operates in animals remains a suggestion, not a result demonstrated by this plant study.