The never ending story of rol genes: a century after

The genes rolA, B, C, and D, derived from Agrobacterium rhizogenes and naturally engineered in plants, are being investigated for a long time about their function, molecular mechanism, origin and evolution and, more recently, the perspectives they offer in plant biotechnology. Evidences point to these genes as important regulators in a wide field of plant endeavors, from hormone control to morphology, from physiological status to defense and from metabolism to signaling. However, in spite of the extant insight on rol genes mechanism and function, a comprehensive picture is still lacking. Recent data suggest that additional research could lead to significant advancement in the knowledge of the role of these genes mainly in plant-bacterium coevolution, and in the development of rol genes-based applications. Through a comprehensive critical review of literature we present a picture of rol genes functions in different plant species, focusing on the relationship between individual genes and plant physiology and metabolism. A possible scenario for their evolution is outlined.