From RolD to Plant P5CS: Exploiting Proline to Control Plant Development.

The capability of the soil bacterium to reprogram plant development and induce adventitious hairy roots relies on the expression of a few root-inducing genes ( and ), which can be transferred from large virulence plasmids into the genome of susceptible plant cells. Contrary to , , which are present in all the virulent strains of and control hairy root formation by affecting auxin and cytokinin signalling, appeared non-essential and not associated with plant hormones. Its role remained elusive until it was discovered that it codes for a proline synthesis enzyme. The finding that, in addition to its role in protein synthesis and stress adaptation, proline is also involved in hairy roots induction, disclosed a novel role for this amino acid in plant development. Indeed, from this initial finding, proline was shown to be critically involved in a number of developmental processes, such as floral transition, embryo development, pollen fertility and root elongation. In this review, we present a historical survey on the rol genes focusing on the role of and proline in plant development.