Resistance against the deadly “Take all” plant disease!

Aakancha Shaw, St. Xavier’s College, Kolkata

The Take all disease is a plant disease that attacks the roots and cereal plants in temperate climates. It is caused by a fungus and all varieties of wheat are susceptible to it.

After extensive research, the researchers have successfully been able to trace the steps of the biological pathway that gives oats resistance to the deadly crop disease- Take all. This discovery has the potent to create opportunities for new ways of defending wheat and other cereals against the deadly soil-borne root disease. The research team already has taken the necessary steps in this aim by successfully reconstituting the self-defense system in the model plant  Nicotiana benthamiana.

Researchers of the National Institute of Botany (NIAB) in Cambridge have initiated experiments to establish the avenacin biosynthetic pathway in wheat’s more complex genome. This was performed to test if it will provide the same resistance to take-all and all other diseases, that shape adaptive evolution and genome architecture and adaptive evolution in plants. Avenacins are a type of antimicrobial compound that are synthesized in the roots of oats where they protect against soil-borne diseases such as take-all. This fungal pathogen causes huge yield losses in wheat and there is no effective means by which it could be controlled. A better understanding of how the avenacins are produced in oats can give scientists the knowledge they need to create disease-resistant lines of wheat by manipulating modern biotechnology.

Earlier experiments were successful in characterizing and cloning ten avenacin biosynthetic pathway genes found in the oat genome. Using a genomics-driven approach, a complete pathway encoded by 12 genes was elucidated. The team found that the genes mentioned above are clustered next to each other in the genome. These are arranged like beads on a string organized along the chromosome. The avenacin gene is very close to the end of chromosome 1 of oats. It is arranged such that the early pathway genes are closer to the end of the chromosome i.e. near the telomere and the late pathway genes are further in. Again, it was established that gene mutations in the late avenacin pathway can result in the accumulation of compounds that could negatively affect plant growth while mutations in the early pathway genes do not. We can infer that a plant is less likely to be affected by toxins if the orientation and arrangement of the genes that are late in the pathway are very much away from the telomere region. This was the conclusion derived. Comparison with the sequenced genomes of other cereals and grasses revealed that the avenacin cluster has formed because of the divergence of oats from the other plant species. 

Plant genomes can evolve their genes to enable them to adapt to particular stresses out here, to soil-borne fungal diseases such as take-all. During this process, winning combinations of genes can provide a selective advantage. These can be recruited and relocated from around the genome and assembled into a cluster like beads on a string. This type of clustering will enable the winning gene-set to be passed on from one generation to generation and mitigate against the incomplete inheritance of the pathway genes that are associated with deleterious effects. The studies demonstrated biosynthetic gene clusters for different types of compounds including drugs.

Again, investigations of how widespread these types of genomic organizations are hinges on the generation of new genome sequences for a wider variety of plants.

Also read:DRDO’s “2-DG” Anti-Covid Drug has been finally launched

Source: Li, Y., Leveau, A., Zhao, Q. et al. Subtelomeric assembly of a multi-gene pathway for antimicrobial defense compounds in cereals. Nat Commun 12, 2563 (2021). https://doi.org/10.1038/s41467-021-22920-8

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