Cut lettuce in the fridge turns yellow within a few days. The leaf isn't simply dying: it switches on a program that breaks down chlorophyll and sends nutrients to other parts of the plant. The conductor of this program is the LsMAX1 gene, which makes the plant produce strigolactone hormones.
When the LsMAX1 gene was switched off, lettuce leaves kept several times more chlorophyll after eight days of darkness. The usual aging genes, such as LsORE1 and LsSGR1, barely turned on in the mutants. But a different set of genes became active: the stress response, including HSP90 and AHA1. The plant didn't stop aging; it chose a different score.
Comparing gene activity showed that the shared part of the aging program remains. Photosynthesis and translation genes switch off the same way in both mutants and normal plants. But the genes that normally destroy chlorophyll stay silent in the mutants. Instead, the stress theme plays.
Previously, strigolactones were thought to simply speed up aging. Now it's clear: they determine which genes get switched on. Losing the signal forces the plant to use a backup pathway linked to stress. This explains why the effect of mutations in these genes can differ between species.
In the future, it may be possible to precisely regulate LsMAX1 activity to extend lettuce freshness without changing the plant's shape. The leaf will stay green longer if the conductor picks the right score.
Strigolactones take their name from the parasitic plant Striga, whose seeds germinate once they sense these compounds in a host's root exudates.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.