Give and take
Survival is the essence of life. This may sound like an abysmal platitude but, in the living world, the act of survival implies an awful lot. To survive, many animals eat other animals, which they must first kill. Birds swallow seeds thus depriving them of a chance to grow into plants. Fungi destroy crops as they use them for their own reproduction. So life, or survival, is also strongly associated with death. A lot is going on at the molecular level too, where myriads of pathways are set into action as a response to nutrition, to infection or to a predator's attack. Plants are intriguing in that their survival cannot depend on mobility: they are unable to flee predators or infection, and quite unfitted to run after prey. Their survival depends on how their stems and leaves develop and move to catch sunlight, for instance, as well as on their means to fight off pathogens. For this, they may even benefit from the help of another species. One example has been described between poplar trees and fungi, in particular the fungus Trichoderma asperellum. T.asperellum, like all fungi, expresses small proteins known as hydrophobins which have a role in fungal growth and defence. One of these hydrophobins, HFB2-6, can prompt poplar signalling pathways that are crucial for the tree's own growth and defence.
