The key is over-expression of the ATHB25 gene. This gene encodes a protein that regulates gene expression, producing a new mutant that gives the seed new properties. Researchers have proven that this mutant has more gibberellin -the hormone that promotes plant growth-, which means the seed coat is reinforced as well.
This mechanism is new, as tolerance to stresses such as aging has always been associated with another hormone, abscisic acid, which regulates defenses based on proteins and small protective molecules, instead of producing the growth of structures like gibberellin does.
Seed germination after the aging treatment. Credit: Universitat Politècnica de València
“The seed coat is responsible for preventing oxygen from entering the seed; the increase in gibberellin strengthens it and this leads to a more durable and longer lasting seed,” explains Eduardo Bueso, researcher at the Institute for Plant Molecular and Cell Biology (IBMCP), a joint center of the Universitat Politècnica de València and the Spanish National Research Council (CSIC), who worked in collaboration with the Unit for Plant Genomics Research of Evry, France (URGV).
The study used the experimental model plant Arabidopsis thaliana, a species that presents great advantages for molecular biology research. Researchers of the IBMCP traced half a million seeds, related to one hundred thousand lines of Arabidopsis mutated by T-DNA insertion, using the natural system of Agrobacterium tumefaciens. “Finally, we analyzed four mutants in the study and we proved the impact on the seed longevity when the overexpression of the ATHB25 gene is introduced,” states Ramón Serrano, researcher at the IBMCP.
Researchers compared the longevity of genetically modified Arabidopsis seeds and seeds which were not modified. In order to do this, they preserved them for thirty months under specific conditions of room temperature and humidity. After thirty months, only 20% of the control plants germinated again, whereas almost the all of the modified plants (90%) began the germination process again.
Researchers of the IBMCP are now trying to improve the longevity of different species that are of agronomical interest, such as tomatoes or wheat.
Biodiversity and benefits for farmers
This discovery is particularly significant for the conservation of biodiversity, preserving seed species and, especially, for farmers.
“In the past, a lot of different plant species were cultivated, but many of them are dissapearing because high performance crops have now become a priority. Seed banks were created in order to guarantee the conservation of species, but they require a periodical regeneration of the seeds. With this mutant the regeneration periods could be extended,” explains Eduardo Bueso.
With regard to farmers, Serrano explains that “the increase of the lifespan of seeds would mean a reduction in their purchase price.”
Citation: Bueso, E., Muñoz-Bertomeu, J., Campos, F., Brunaud, V., Martínez, L., Sayas, E., Ballester, P., Yenush, L., Serrano, R. (2014). Arabidopsis thaliana HOMEOBOX 25 uncovers a role for gibberellins in seed longevity. Plant Physiology 164: 999 1010.