Two auxins are better than one: BiAux joins forces with auxin to enhance lateral root formation

The iterative formation of lateral roots (LRs) during plant life span allows the exploration of new sources of nutrients and water.Auxin plays a key role in all major stages of lateral root formation.Auxin signal is required for priming pericycle cells into LR founder cells (FC), LR primordium initiation, morphogenesis and emergence (Du & Scheres, 2018).In Arabidopsis thaliana, LRs are set along the primary root by a mechanism known as "root clock," where a periodic gene expression in phase or antiphase with an auxin signal peak oscillates in a position close to the primary root tip, named the oscillation zone (OZ).This oscillatory behavior results in the establishment of a pre-branch site, a position where pericycle cells with a memorized priming signal initiate a LR primordium later on (Reyes-Hernández & Maizel, 2023).During LR development, auxin signal is mainly transduced through the formation of a coreceptor by TRANSPORT INHIBITOR RESPONSE1 (TIR1) or its closest paralogues AUXIN SIGNALING F-BOX (AFB1 to AFB5) proteins and Aux/IAA family proteins, where auxin plays a role as the molecular glue for this assembling (Tan et al., 2007).When low levels of auxin are present in cells, Aux/IAA proteins tend to dimerize with AUXIN RESPONSE FACTOR (ARF) transcription factor family members, repressing ARF activity.Once auxin levels are increased, Aux/IAA proteins are targeted for degradation, releasing ARF proteins to regulate the transcription of their target genes (Tiwari et al., 2003;Zenser et al., 2001).