Symbiosis and the social network of higher plants.

In the Internet era, communicating with friends and colleagues via social networks constitutes a significant proportion of our daily activities. Similarly animals and plants also interact with many organisms, some of which are pathogens and do no good for the plant, while others are beneficial symbionts. Almost all plants indulge in developing social networks with microbes, in particular with arbuscular mycorrhizal fungi, and emerging evidence indicates that most employ an ancient and widespread central 'social media' pathway made of signaling molecules within what is called the SYM pathway. Some plants, like legumes, are particularly active recruiters of friends, as they have established very sophisticated and beneficial interactions with nitrogen-fixing bacteria, also via the SYM pathway. Interestingly, many members of the Brassicaceae, including the model plant Arabidopsis thaliana, seem to have removed themselves from this ancestral social network and lost the ability to engage in mutually favorable interactions with arbuscular mycorrhizal fungi. Despite these generalizations, recent studies exploring the root microbiota of A. thaliana have found that in natural conditions, A. thaliana roots are colonized by many different bacterial species and therefore may be using different and probably more recent 'social media' for these interactions. In general, recent advances in the understanding of such molecular machinery required for plant-symbiont associations are being obtained using high throughput genomic profiling strategies including transcriptomics, proteomics and metabolomics. The crucial mechanistic understanding that such data reveal may provide the infrastructure for future efforts to genetically manipulate crop social networks for our own food and fiber needs.