Strigolactone receptor DAD2 promotes lateral root formation in Petunia hybrida

Strigolactone regulates various aspects of plant development and interactions with beneficial microbes. While the role of SL in shoot development is highly conserved between monocots and dicots, its role in root system architecture is controversial and context-dependent, although most of the SL appears to be produced there. A central parameter in plant fitness is root-to-shoot ratio, which is determined by growth and branching activity of both, the root as well as the shoot. We used previously characterized mutants defective in SL biosynthesis and sensing to test the role of SL in root growth and branching. Here, we show that a mutant defective in the petunia strigolactone receptor (dad2) exhibits defects in root meristem activity and root branching. Notably, this phenotype is not observed in the SL biosynthetic mutant dad1, suggesting that DAD2 may perceive a strigolactone analogue that is produced in a DAD1-independently fashion. DAD2 is induced in cortex cells adjacent to lateral root primordia, where it allows them to penetrate the cortex and to grow out of the main root. We propose a model by which inducible SL perception in cells adjacent to LRPs promotes auxin-induced cell wall remodeling in the cortex to allow passage of lateral roots. 1-sentence summaryLateral roots are initiated inside the main root, hence, they have to penetrate several cell layers to grow out. We propose that strigolactone cooperates with auxin to mediate lateral root emergence.