Root Branching: Traditional Pathways and Beyond

Plant root branching is characterized by an interplay of genetic regulators and environmental cues. Traditionally, the genetic regulators, PLETHORA 3/5/7 and WOX11/12, are required for lateral root and adventitious (lateral) root formation in Arabidopsis, respectively. However, simultaneous loss of these five regulators did not abolish root branching, indicating that additional pathways are involved in root branching. To explore potential regulators, we identified the new plant-growth-promoting rhizobacterium, CM11, which significantly induced lateral root formation while inhibiting primary root growth. Further exploration showed that CM11 emitted volatile organic compounds that altered root architecture, and we identified the Arabidopsis methylesterase MES9 as being involved in this response. In addition, we uncovered roles for the mobile florigen FT and its antagonist TFL1 in modulating root architecture. Together, these findings show that multiple genetic and environmental factors provide developmental plasticity beyond the established PLT and WOX pathways.