Argentina
March 31, 2022
>> Mejoramiento de cultivos: descubren cómo hace la planta de porotos para dejar entrar a las bacterias de suelo que más la benefician
Eugenia Zanetti and Flavio Blanco, two of the authors of the work, in the IBBM laboratory. Credits: CONICET Photography
Crop improvement is an ancient technique that through different procedures of varying complexity pursues a specific objective: to optimize the productivity of a species, enhancing its most valued qualities, increasing its resistance to pests and extreme climatic factors, and enhancing its efficiency in the use of resources. Thus, this practice can be developed both through the manual crossing of the most vigorous specimens to obtain superior quality seeds, and through sophisticated biotechnological methods that explore more challenging possibilities.
This is the case of the massive sequencing of ribonucleic acid (RNA), a tool that shows which genes are activated in different types of cells, on what occasions and in what way. It allowed a research team from the ‘Instituto de Biotecnología y Biología Molecular (IBBM, CONICET-UNLP)’ to identify small RNAs –molecules that carry genetic information– capable of modulating the establishment and efficiency of the symbiosis between the black bean plant (Phaseolus vulgaris) and nitrogen-fixing bacteria. The study was published in the prestigious journal New Phytologist.
“In recent years, small RNAs have emerged as key regulators of gene expression or activation that control multiple processes. Knowing which ones are involved in each case allows us to develop improvement strategies, such as the exogenous application, that is, from outside, of RNAs directly on the plants, which has made it possible to overcome the resistance of certain groups to other technologies, such as genetic modification,” explains Flavio Blanco, CONICET researcher at the IBBM and one of the authors of the paper. The study specifically focused on the establishment of nitrogen-fixing symbiosis, a process that occurs in legumes under conditions of low availability of this chemical in the soil.
Like any symbiosis, it is an intimate association of organisms of different species in which both benefit mutually. During the process, the bacterium infects the root and is housed within a specialized organ for nitrogen fixation called nodule. “This mechanism allows legumes to obtain a nitrogen source that can be incorporated into proteins and nucleic acids, which is vital for its development and growth. Besides, the bacterium is favored and survives thanks to the carbon coming from the photosynthetic products synthesized by the plant,” María Eugenia Zanetti explains. She is a CONICET principal investigator at the IBBM and also author of the work.
According to the study, the black bean is able to preferentially select and host those bacteria that are more efficient in the formation of nodules, thus increasing the mass production of the plant. The scientists managed to identify a small RNA that responds specifically to these bacteria, which they called miR5924. In this way, most of the nodules are occupied only by these symbiotic microorganisms. “Our work showed that if plants produce high amounts of this RNA, the nodules can be infected promiscuously, that is to say, simultaneously by two different bacteria regardless of whether they are more or less efficient at forming nodules.” Zanetti explains.
“Legumes differentiate beneficial bacteria from pathogenic or harmful ones, and this recognition involves specific signals present or produced by the bacteria, triggering a local or partial suppression of the defense that allows the entry of beneficial organisms. To be more specific, the bean plant has the ability to differentiate the bacterial strains that fix nitrogen more efficiently, and it is there that certain small RNSs would modulate the defense response, allowing these bacteria to access the roots to begin the symbiosis,” Blanco describes.
As regards the possible applications that could derive from this discovery, the experts emphasize that small RNAs are important modulators of plant growth and development, and have been applied to improve agronomically important traits such as tolerance against drought and resistance to pathogens. “This study opens up the possibility of using strategies based on these small RNA molecules to optimize the nitrogen-fixing symbiosis and increase not only the production of legumes, but also the incorporation of nitrogen in soils subjected to agricultural practices,” explain the authors.
“Legumes are the most important plants for agriculture in the world after cereals, which unlike the latter; they have not received as much attention during the modernization of agricultural techniques developed in the last century during the so-called ‘green revolution.’ This means that there is great improvement potential for these vegetables, which could strongly contribute to the development of more environmentally friendly technologies. The challenge is to transfer the discoveries from the laboratory to the crops and to know how possible it is to transfer the new knowledge about beans to other species of the same family,” conclude the scientists.
By Mercedes Benialgo
English version: Cintia González
References:
Castaingts Melisse, Kirolinko Cristina, Artunian Jennifer, Rivero Claudio, Villagra Mancini Ulises, Blanco Flavio, Zanetti María Eugenia. Differential analysis of host small RNAs identified conserved and new miRNAs that affect nodulation and strain selectivity in the Phaseolus vulgaris- Rhizobium etli symbiosis. DOI: https://doi.org/10.1111/nph.18055.
About the study:
Melisse Castaingts. Doctoral fellow at the moment of publication. IBBM.
Cristina Kirolinko. Doctoral fellow. IBBM
Jennifer Artunian. Doctoral fellow. IBBM.
Claudio Rivero Hernández. Doctoral fellow. IBBM.
Ulises Villagra Mancini. Associate professional. IBBM.
Flavio Blanco. Independent researcher. IBBM.
María Eugenia Zanetti. Principal researcher. IBBM.
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