Plants synthesize ergothioneine, showing a link to abiotic stress.

Ergothioneine (EGT) is a sulphur-containing histidine derivative and a potent antioxidant that exhibits beneficial effects on human health. Thus far, only fungi and certain bacteria have been reported to produce EGT, whereas plants are assumed to rely on an uptake of EGT. Here, the presence of EGT biosynthetic genes and their functionality were investigated in Viridiplantae. The biosynthetic genes EGT1 and EGT2 from yeast were used for transcriptome and genome analyses in evolutionarily informative species across Viridiplantae. Targeted metabolomics (HPLC-MRM/MS) was used to quantify EGT in selected algae and land plants grown under control conditions and exposed to abiotic stress. EGT1 and EGT2 genes were identified in streptophyte algae, bryophytes, lycophytes, monilophytes, and gymnosperms. Targeted metabolomic profiling demonstrated endogenous EGT production in diverse algae and land plants, refuting the long-standing view that plants cannot synthesize this antioxidant. Notably, EGT1 genes do not exist in angiosperms, which likely lost this gene and the capability to synthesize EGT. After high light and heat stress exposure, EGT synthesis increases significantly in the streptophyte algae Klebsormidium nitens and the moss Physcomitrium patens, suggesting that EGT also exerts an antioxidant function in plants. Contrary to previous assumptions, various plants possess EGT genes and are capable of synthesizing EGT. Abiotic stress experiments reveal a link between EGT and the plant stress response, opening new avenues for research in stress signalling and adaptation - areas that are also relevant for enhancing crop resilience and nutritional quality.