Self and Non-self DNA
From the breakthrough discovery of the self-DNA inhibition to the understanding of the molecular mechanisms behind the phenomena.
New perspectives about extracellular DNA
Self-DNA inhibition
In recent years, several studies have shed light on the species-specific inhibitory role of extracellular DNA. It has been observed that many types of living organisms, including plants, algae, fungi, and animals, are inhibited at the cellular level by the presence of fragments of their own DNA (self-DNA) in the environment, either substrate or food.
In the case of animals, for example, when fruit flies (Drosophila melanogaster) are exposed to self-DNA added to their food, there is a significant reduction in reproduction, delayed development, and early mortality at a macroscopic level, while in the flesh fly (Sarcophaga carnaria), larval metamorphosis is interrupted by feeding with their self-DNA, resulting in death during the pupal stage. Negative effects have also been observed in nematodes, such as Caenorhabditis elegans, which show increased mortality and malformations in the progeny. Ongoing studies are producing comparable results for other animals, including some model species of fish (Zebrafish and Nothobranchius furzeri) and shrimp and their parasites (Neocaridine and Planaria).
In fungi, the enrichment of growth substrates with their self-DNA drastically reduces spore germination and mycelial development. This effect is very similar to what has been observed in seeds and plant roots and provided the explanatory mechanism for the origin and development of the so-called “fairy rings”.
The phenomenon has been experimentally demonstrated in field conditions and widely modelled in theoretical and mathematical investigations. These consistent and robust body of evidences support the logic explanations of two phenomena of great scientific interest: “plant-soil negative feedback” studied in plant ecology and “soil-sickness” in agriculture.
The self-DNA inhibition (autotoxicity) can be seen as a general biological law which unifies the growth/developmental dynamics at cell and population level and the pattern formation processes at ecosystem scale into one model.
Mazzoleni et al. Inhibitory effects of extracellular self-DNA: a general biological process?.
New Phytologist 2015
Understanding why
For a long time, research has been dedicated to identifying the causal factor of species-specific inhospitability. As early as the 19th century, the Swiss botanist Augustin Pyrame de Candolle, hypothesized the release of particular species-specific phytotoxins by plants as the cause of this phenomenon. This hypothesis generated enthusiasm among generations of scientists and technicians struggling to identify the chemical nature of these toxins and this flourished in the field of phytochemistry and the study of allelopathy. A breakthrough was recently made by the Ecology and Modelling group at the University Federico II of Naples, led by Professor Stefano Mazzoleni, with the discovery of the inhibitory effect of self-DNA, highlighting the occurrence of autotoxicity, i.e. “autopathy”, instead of allelopathy.
DNA, the species-specific molecule par excellence, is fundamental for all cellular activities in living organisms, but it is also dispersed into the environment after the death and decomposition of organisms or their parts and the DNA fragments are particularly resistant to degradation and can accumulate in soils over years. However, they are water-soluble, and so they can be easily washed away in case of flooding and water flows.
This characteristic helps to explain why rings of vegetation are primarily observed in semi-arid environments, where the scarcity of precipitation leads to little washing away of self-DNA. In agriculture, it may also explain why rice, grown in periodically flooded paddies where DNA is repeatedly washed away, can be cultivated repeatedly without crop rotations or fallow periods – an unfeasible practice with other cereal crops or even rice when grown in dry conditions.
Chiusano et al. Arabidopsis thaliana Response to Extracellular DNA: Self Versus Nonself Exposure.
Plants 2021.
Self-DNA inhibition
In recent years, several studies have shed light on the species-specific inhibitory role of extracellular DNA. It has been observed that many types of living organisms, including plants, algae, fungi, and animals, are inhibited at the cellular level by the presence of fragments of their own DNA (self-DNA) in the environment, either substrate or food.
In the case of animals, for example, when fruit flies (Drosophila melanogaster) are exposed to self-DNA added to their food, there is a significant reduction in reproduction, delayed development, and early mortality at a macroscopic level, while in the flesh fly (Sarcophaga carnaria), larval metamorphosis is interrupted by feeding with their self-DNA, resulting in death during the pupal stage. Negative effects have also been observed in nematodes, such as Caenorhabditis elegans, which show increased mortality and malformations in the progeny. Ongoing studies are producing comparable results for other animals, including some model species of fish (Zebrafish and Nothobranchius furzeri) and shrimp and their parasites (Neocaridine and Planaria).
In fungi, the enrichment of growth substrates with their self-DNA drastically reduces spore germination and mycelial development. This effect is very similar to what has been observed in seeds and plant roots and provided the explanatory mechanism for the origin and development of the so-called “fairy rings”.
The phenomenon has been experimentally demonstrated in field conditions and widely modelled in theoretical and mathematical investigations. These consistent and robust body of evidences support the logic explanations of two phenomena of great scientific interest: “plant-soil negative feedback” studied in plant ecology and “soil-sickness” in agriculture.
The self-DNA inhibition (autotoxicity) can be seen as a general biological law which unifies the growth/developmental dynamics at cell and population level and the pattern formation processes at ecosystem scale into one model.