Every plant cell has an orchestra where the musicians are the same, but the scores differ from species to species. The star instrument of this orchestra is the proteasome, a large protein machine that destroys tagged proteins. It exists in all living things, and its design has barely changed over millions of years. But in plants, the number of genes encoding the parts of this machine varies widely, and for a long time scientists couldn't figure out why.

Scientists compared the genomes of 18 plant species, from algae to flowering plants. They found that 16 of the 18 species have duplicated proteasome genes, that is, gene copies that arose recently and independently in different lineages. The proteins themselves barely changed: only 4 cases out of 886 showed signs of positive selection. Regulation, however, diverged a lot: paralogs responded differently to stress. In the promoters of proteasome genes in angiosperms, a motif called PRCE is enriched, and it is recognized by the NAC53/78 factors as well as by the TRB1/3/5 proteins. These proteins normally protect chromosome ends, but it turned out they can switch on proteasome genes. The trb4 trb5 mutants became hypersensitive to a proteasome inhibitor, and their induction of proteasome genes was disrupted.

It's as if the musicians in the orchestra stayed the same, but the conductor kept changing the scores: in one species the proteasome is more active in response to drought, in another to cold. Understanding proteasome regulation could help breed stress-resistant plants, since proteostasis is critical for surviving harsh conditions. For now this is fundamental knowledge, but it points the way for applied work.

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