Lettuce loses its market-ready look fast after cutting: the leaves yellow as chlorophyll breaks down. Strigolactones were already known to speed up aging in model plants, but their role in vegetable crops had never been tested. On top of that, in some species mutations in these genes had no effect on aging at all, which cast doubt on how universal the mechanism really is.
The researchers created lettuce mutants with CRISPR/Cas9, knocking out the LsMAX1 gene. Leaves from wild-type and mutant plants were kept in the dark for 8 days, after which chlorophyll content and gene activity were measured. For comparison, they also used Arabidopsis carrying the same gene introduced from lettuce, and treated leaves with the synthetic strigolactone GR24.
After 8 days of darkness, Lsmax1 mutant leaves held on to significantly more chlorophyll than ordinary plants did. Aging-related genes (LsORE1, LsSGR1) were barely activated in the mutants. RNA analysis, however, showed that a distinct group of stress-response genes switches on in the mutants, including HSP90 and AHA1. Even so, the overall aging program is partly preserved: photosynthesis and translation genes shut down the same way in both genotypes.
The work shows that strigolactones don't merely accelerate aging; they determine which genes get switched on. Lose that signal, and the plant is forced onto an alternative, stress-related path. This changes how we think about the role of hormones in aging and explains why the effects can differ from one species to another.
Looking ahead, it should become possible to fine-tune LsMAX1 activity to extend lettuce freshness without altering the plant's shape. It will also be important to study how this mechanism works in other leafy vegetables, spinach or arugula, for instance.
The results could be used in breeding lettuce and other leafy crops for longer shelf life. They also matter for the fundamental biology of plant aging.
Strigolactone and carbohydrate levels in the leaves need to be measured during storage, and the function of the D14 receptor and the MAX2 protein in lettuce should be checked. In addition, a time-course transcriptome analysis is worth doing to separate primary effects from secondary ones.
The work links hormonal regulation to the choice of a transcriptional aging program. What remains open is exactly how strigolactones interact with other signals, ethylene and salicylic acid among them, and why the response varies between species.
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.