The microRNA156/SPL9module mediates auxin response to facilitate apical hook maintenance inArabidopsis

Abstract

ABSTRACTAuxin coordinates cell growth by promoting or inhibiting cell expansion during etiolated seedling development, but whether and how microRNA modules participate in this process remains unclear. Here, we show the miRNA156/SQUAMOSA PROMOTER-BINDING-PROTEIN-LIKE9(miR156/SPL9) module is critical for skotomorphogenesis. Perturbation of the miR156/SPL9module affected skotomorphogenesis, as the loss of miR156 function orSPL9de-repression led to shorter hypocotyl, higher hook angle, and delayed hook opening. Opposing phenotypes were observed in dark-grownspl9and miR156-overexpressing seedlings. Importantly, loss of miR156-dependentSPL9regulation triggered apical hook formation even under reduced levels of endogenous auxin. miR156-targetedSPL9arrested cell expansion by repressingsmall auxin-up RNA19(SAUR19) gene in aFRUITFULL(FUL)-dependent and independent manner. The conserved miR156/SPL9/15module also affects skotomorphogenesis in tomato, impacting its successful soil emergence. Our findings unravel how the miR156/SPL9module plays a pivotal role in the auxin network coordinating apical hook development to enable appropriate seedling emergence.