Reaserchers at UNLP discovered an small RNA molecule that allows to improve the productivity of bean plants
Making use of modern technologies of massive RNA sequencing, a group of researchers from the Institute of Biotechnology and Molecular Biology (IBBM), belonging to the Faculty of Exact Sciences of the National University of La Plata (UNLP-CONICET) identified a small ribonucleic acid (RNA) capable of improving the growth of the black bean plant.
In Argentina, legume crops include peas, chickpeas, lentils and beans and they are characterized by having a high export profile, although with marked differences depending on the species in question. Foreign sales of black beans during 2020 represented 40% of the volume and 30% of the value of the exports of the complex (170 thousand tons; 111 million dollars respectively), being the main destination of the same Brazil (50 % of the volume and 45% of the value), followed far behind by Venezuela and Cuba.
Dr. María Eugenia Zanetti, director of the project, explained that "the RNAs discovered in the roots of the bean plant are capable of modulating the establishment and efficiency of the symbiosis between the legume plant Phaseolus vulgaris (bean) and fixing bacteria. of nitrogen”.
"This type of symbiosis allows the leguminous plant to obtain a nitrogen source that can be incorporated into proteins and nucleic acids, which is crucial for the development and growth of the plant, and therefore to sustain agricultural production." On the other hand, the symbiotic bacteria are favored with a carbon source from the photosynthetic products synthesized by the plant. During the establishment of the nitrogen-fixing symbiosis, the bacterium infects the root of the plant and is housed within a specialized nitrogen-fixing organ called a "nodule".
Dr. Zanetti added: “The black bean plant is able to preferentially select and host those bacteria that are more efficient in nitrogen fixation, thus increasing the mass production of the plant. In this way, most nodules are occupied only by the symbiotic bacteria that are most efficient at nodule formation. In the study we carried out, a small RNA was identified that responds specifically to the most efficient bacteria in the formation of nodules.
The IBBM research group demonstrated that, if plants produce high amounts of this small RNA, the nodules can be infected promiscuously by both the most efficient bacteria and the least efficient one. Moreover, nodules of the plants that overproduce of this small RNA are simultaneously occupied by two different bacteria, that is, nodules that are infected by the most efficient and the least efficient bacteria at the same time (see illustration) This small RNA might act by suppressing plant's defenses when the more efficient bacterium infects the plant thus allowing the bacteria to enter and occupy the nodules.
In the illustration, nodules were infected with bacterial strains labeled with either red or green fluorescent proteins.
Small RNAs have emerged as important modulators of plant growth and development and have been used to improve agronomically important traits such as drought tolerance and pathogen resistance.
This study opens the possibility of using strategies based on small RNAs to improve the nitrogen-fixing symbiosis and increase not only the production of legumes, but also the incorporation of nitrogen in the soils used in agricultural practices.
The discovery was published today March 28yh in the science journal New Phytologist under the title 'Identification of conserved and new miRNAs that affect nodulation and strain selectivity in the Phaseolus vulgaris–Rhizobium etli symbiosis through differential analysis of host small RNAs'".