How a genetic split helped plants conquer polluted soils

Phytochelatin synthases (PCS) produce phytochelatins, tiny cysteine-rich peptides that bind and neutralize toxic metal ions such as cadmium and arsenic. These molecules act as the plant's natural detoxification system, sequestering harmful elements into vacuoles to prevent cell damage.

Although previous studies have examined individual PCS genes in model plants such as Arabidopsis thaliana (AtPCS1, AtPCS2), the broader picture of how PCS genes have diversified across plant evolution remained unclear.

Without realizing it evolutionary historyit has been difficult to explain why plants vary so much in metal tolerance. Based on these issues, researchers sought to find out how gene duplication and functional divergence has shaped the evolution of PCS around the world. plant genomes.

A research team from the Edmund Mach Foundation and the University of Pisa traced the evolutionary origins of metal detoxification mechanisms in plants.

Their conclusionspublished in Horticulture Researchshowed that a long-forgotten duplication of PCS genes occurred early in the evolution of flowering plants.

By combining genome-wide phylogenetic reconstruction with laboratory and plant-level experiments, the researchers discovered how this duplication—the split into the D1 and D2 lineages—allows plants to fine-tune their biochemical defenses against heavy metal stress.

The study analyzed more than 130 complete plant genomes to map the evolutionary path of PCS genes. The researchers discovered an ancient duplication, called the “D duplication,” that arose during the early diversification of eudicots and persists to this day. This event divided the PCS genes into two families: D1 and D2.

To study their functions, the team isolated MdPCS1/MdPCS2 from apple and MtPCS1/MtPCS2 from barrel medic and introduced them into Arabidopsis thaliana mutants lacking native PCS activity. Laboratory assays showed that D2 type PCS enzymes were significantly more active than their D1 counterparts, demonstrating an increased ability to synthesize phytochelatins and sequester cadmium and arsenic.

In living plants, D2 genes provide stronger growth recovery and higher resistance to metal stress, while D1 genes maintain overall thiol balance and moderate detoxification capacity. Sequence analysis revealed two key amino acid residues likely responsible for their functional divergence.

The results show that both types of genes were retained because their complementary roles enabled efficient detoxification—a remarkable example of the evolutionary fine-tuning that continues to protect modern crops.

“Our results show how evolution has refined a vital survival mechanism,” said Dr Claudio Varotto, co-author of the study.

“Two copies of the PCS gene coexist for over a hundred million years because they complement each other: D1 provides stability and D2 provides power. This dual system gives plants the flexibility to adapt to a range of metal-related challenges. This is a wonderful illustration of how ancient genetic innovations continue to shape plant resilience today.”

This discovery not only deepens our understanding of plant evolution, but also opens new avenues for sustainable agriculture. By targeting the expression of PCS genes or transferring D2-type PCS activity to sensitive crops, breeders can create varieties that thrive in contaminated soils while reducing the accumulation of heavy metals in edible parts.

Such genetic discoveries could also improve phytoremediation strategies, which use plants to clean up polluted environments.

As the world faces increasing soil pollution, understanding how plants have evolved to tolerate toxic metals offers both scientific inspiration and practical tools for a safer agricultural future.