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Brazil is involved in new discovery on the defense mechanism of plants

A group of scientists from the Netherlands, Brazil and the United States, with the participation of Embrapa Environment (SP), has discovered that plants, when attacked by pathogens at its roots, are able to interact with the soil fungi and bacteria in order to protect themselves from diseases in a much more complex and large scale than what was already known by science. The exploitation of these mechanisms opens possibilities for the control of agricultural diseases and pests, including the discovery of new molecules. Studies of this type pave the pathway for a more sustainable agriculture, reducing the need of chemicals for the control of diseases.

Published in Science magazine, the paper describes how the microbial flora living inside the roots naturally defends the plants against the invasion of pathogens that cause diseases, which is an unprecedented discovery.

In 2011, the team had already published another paper also in Science, in which they described the way plants control the recruiting of beneficial bacteria from the rhizosphere, which is the closest soil to the roots, and use them to protect themselves from diseases.

The third line of defense

In the new work, the scientists wanted to expand the comprehension on the complex interaction between the plant and its microbiome. With this purpose, they investigated the pathogens that reached the inside of roots. For that, microorganisms have to transpose the rhizosphere (first line of defense) and the plant’s tissue (second line of defense). In this work, researchers have discovered a third line of defense against infections: a modulation of the microbiome living inside the roots.

The applied method used the metagenomics and the complex network inference approaches, in order to guide the construction of a consortium of Chitinophaga and Flavobacterium bacteria, inserting them in the roots to neutralize the disease. Later, the group used the CRISPR technique to confirm that the NRPS-PKS gene group was responsible for the suppression of the disease in the plant’s interior.

In practice, the results highlighted that the endophyte microbiome of the roots shelters a variety of still not widely known functional characteristics – which, when put together, can protect the plant from inside out.

The Embrapa researcher Rodrigo Mendes, one of the authors of the paper, states that this study represents a landmark in the research of plants’ microbiomes. “For a long time now we have known the importance of entophytic microorganisms for the promotion of growth and for the health of plants, but we still know very little about the genomic and functional diversity of the endophyte microbiome and its interactions with the plant and pathogens. By following the steps of the fungus when infecting the plant, we dissected the process and used advanced molecular techniques to elucidate the mechanisms governing the plant’s defense”, he revels.

The discovery of defensive bacteria

The investigation focused in the functional potential of the root’s microbiome in the protection of plants against fungi infections. By using advanced techniques from different approaches (such as network inferences and metagenomics), the scientists have identified consortiums of bacteria found in soils that are unfavorable (suppressive) to the development of the Rhizoctonia solani fungus, which causes diseases in several plants, such as rice, wheat and sugar beet. The techniques were also employed to identify groups of functional genes of the microorganisms that inhabit these soils.

The scientists analyzed the beet seedlings cultivated in a soil suppressive to R. solani in order to identify the microorganisms associated to the suppression of diseases, characterizing groups of biosynthetic genes (BGCs). The next step was to rebuild the synthetic consortium of entophytic microorganisms and, finally, to direct the mutations to test the role of specific BGCs in response to the disease.

The experiments showed that, under the invasion of pathogens, bacteria of the Chitinophagaceae and Flavobacteriaceae genus enriched themselves in the core of the plant and attacked the fungus. They presented improved enzymatic activities, which caused the degradation of the fungi cell wall. We still do not know where these two bacterial genus are located in the root tissue and how they interact in the molecular level of the core.

“The results of this study highlighted the abundance of microbiome genus that are still unknown and their functional characteristics in the entophytic microbiome of the root, issues that stimulate the continuity and the deepening of these studies”, states Mendes.

Source: Embrapa, Marcos Vicente (MTb 19.027/MG) from Embrapa Environment


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