HYBRID FORMATION. “It can be proposed that numerous invasions of ancient roots via bacteria and especially fungi resulted in generation of abundant host-pathogen synapses which transformed later into the symbiotic and, finally, into the auxin-secreting root synapses most active in epithel-like epidermis and endodermis at and around the transition zone.”
http://journal.frontiersin.org/article/10.3389/fcimb.2013.00044/full