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Untouchable Friends: plants and bacteria exchange genes

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All living organisms somehow interact with others; and one of the closest relationships is symbiosis, which means ¨living together¨. An example of symbiosis is our relationship with the collective group of bacteria that compound the microbiota in our skin, mouth, gut, and other body parts. This microbiota helps us to prevent infections, and maintain healthy tissues, and bacteria living happily in our body since they have all the adequate conditions such as nutrients, temperature, pH, etc. However, this kind of interaction is not human-exclusive, plants also have microbiota, and this symbiotic interaction promotes wellness on both sides of the plants and bacteria.

Arabidopsis thaliana is the most used plant model; thus, its microbiome is also well-studied. A recent study published by Shelly Haimlich and collaborators analyzed the genomic sequences from A. thaliana and its microbiota members. The researchers found that A. thaliana and its microbiota transferred 75 genes between each other; bacteria transferred 59 genes to A. thaliana, and in return, received 16 genes. This phenomenon is known as horizontal gene transfer (HGT).

Most of these genes are related to carbohydrate functions, which are important for many energetic and structural functions in plants and bacteria. Interestingly, bacteria transferred genes related to auxin biosynthesis, the plants’ growth hormones, to the plant. The current study is thought to be evidence of HGT being a consequence of coevolution, and show that this transference of genes is beneficial to both sides. To evaluate the implication of HGT, the researchers studied whether the DET2 gene from the plant found in bacteria performs the same function in the plant. The DET2 gene is essential for plant growth since it is involved in phytohormone biosynthesis, and the loss of this gene in the plant results in dwarfism. To test this, the researchers generated a mutant plant (det2) that does not express the DET2 gene; a mutant expressing the DET2 bacteria gene instead of the DET2 gene from the plant (IfDET2-NG). They found that, as expected, the det2 mutant is smaller than the wild-type (WT) plant, that is without mutations. The IfDET2-NG mutant plant grew almost like the WT, indicating that the DET2 bacteria gene conserves the original functions of the DET2 plant gene.

The findings of this research show how symbiotic organisms become untouchable friends by sharing essential genes in both directions through HGT. This allows, in case one organism loses these essential functions, their friend organisms to supply this function and help the affected organism survive, thus ensuring its evolutive success.