An endophyte is an organism which lives inside a plant; the term literally means “inside plant.” Some are parasitic in nature, taking advantage of the plant as a supply of nutrients or energy, while others form a mutualistic relationship with their hosts, performing a function which confers a benefit to the host plant. For example, an endophyte may secrete chemical compounds which deter other plants, eliminating resource competition for the host plant.
The practice of endosymbiosis, as it is known, is relatively common in the natural world, and appears to be extremely ancient as well. Smaller organisms live inside larger ones in a variety of settings, from the depths of the oceans to the rocks on the highest mountains. A very well known example of endosymbiosis is lichen. Lichen is actually a composite of two different organisms: a fungus and an endosymbiote such as an algae or cyanobacterium.
In the case of endophytes, the most famous example is probably fescue grass. Some fescue is colonized by fungi which appear to make the grasses stronger, more durable, and able to resist tough climates. Not only that, but livestock tend to prefer fescue with an endophyte, suggesting that the fungus confers additional nutritional value or flavor which makes the colonized grass appealing to animals. Numerous studies have been conducted to examine how fescue colonized with fungi grows, and to determine the difference between colonized and uninfected fescue.
Researchers are always interested in identifying new endophytes and learning about their effects on the plants they live in. In the case of mutualistic relationships, endophytes can be a very valuable survival tool for plants colonized with them, as the organism benefits the plant in some way through colonization. A species which acts as an endophyte can move through a plant population in a variety of ways, depending on the plant and the organism in question.
Bacteria and fungi are the most common endophytes. Both are small enough to live comfortably inside a host plant, and both are also famous for their adaptability and readiness to take advantage of situations which may be beneficial. Fungi and bacteria can also produce a range of secretions which can include toxins as well as beneficial compounds. Establishing a mutualistic relationship is beneficial to both species, increasing their chances of survival in the long term by ensuring that both endophyte and colonized plant are able to survive in a variety of environments.