Scientists have wondered whether the microbiome of plants is due to nature or food. Research at Stockholm University, published in Environmental microbiologyshowed that acorns contain a wide variety of microbes and that oak seedlings inherit their microbiome from these acorns.
"The idea that seeds can be the link between the microbes in the mother tree and its offspring has been widely debated, but this is the first time anyone has demonstrated the path of transmission from the seed to the leaves and roots of emerging plants," says Ahmed Abdelfattah, Researcher at the Institute for Ecology, Environment and Plant Sciences (DEEP) at Stockholm University.
The microorganisms found on the seed are often valuable to the plant, promote its growth and protect it from certain diseases. Each species of plant is home to its own microbial community, with some of the microbes living on its surface and others in the plant's tissues.
The finding also means that the microorganisms from the seed, since they are present first, can represent a barrier that influences the subsequent colonization by other microbes from the environment. The experiment was carried out in oak trees as it is one of the most abundant tree species in Swedish and European forests.
"The microorganisms from the seed are also expected to be very important to the health and function of the plants," says Ahmed Abdelfattah.
The fossil record shows that plants have been associated with the fungi and bacteria that make up the microbiome for more than 400 million years. Several species that the scientists found on the oak kernels have already shown in other studies that they are involved in protection against various plant pathogens, in promoting growth, in nitrogen fixation and in the detoxification or biodegradation of toxic environmental pollutants.
Evidence of heredity in natural conditions is challenging as seeds are exposed to and depend on their environment as they germinate, particularly the soil, which has a microbially rich environment. It is therefore almost impossible to distinguish which microorganisms actually originate from the seed or the soil. The research team therefore used a novel cultivation device to grow oak seedlings in a microbe-free state and to keep the leaves separated from the roots. This enabled them to be sure that the microorganisms were from the seed and that they could demonstrate that some seed microorganisms migrated to the roots and others to the leaves.
"It is already known that plant leaves and roots host different microbial communities, as several recent studies have shown. However, in this study we were surprised to see that this is also the case at an early stage of plant development and that the seeds at least could." be partly responsible for these differences, "says Ahmed Abdelfattah
"Several breeding companies incorporate the seed microbiome into their programs in the hope of having superplants with better genes and better microbes. One technique used is to treat seeds with beneficial microorganisms with the aim of these microbes eventually colonizing the plant and exerting themselves their effects throughout the life of the plant, "says Ahmed Abdelfattah.
The next step for the research team is now to identify which main source is the microbiome – the environment or the seeds.