<i>SHOOT GRAVITROPISM 9</i> links sensory timing to the initial lateral root growth angle.

Abstract

Plants strategically respond to gravity and actively set defined growth angles. These gravitropic set-point angles (GSAs) shape the width and depth of the root system, determining soil exploration for water and nutrient uptake. Despite its physiological importance, the concept by which lateral roots establish their growth angle has remained largely unclear. Here, we show that temporal regulation of gravity responsiveness within a defined developmental phase sets the initial GSA in lateral roots. Stage-specific transcriptome profiling revealed that <i>SHOOT GRAVITROPISM 9</i> (<i>SGR9</i>) is upregulated in emerged lateral roots as they first respond to gravity. Loss of SGR9 slows amyloplast sedimentation and delays the PIN3-dependent establishment of asymmetric auxin distribution. Notably, the delay in the gravity response alters, rather than merely postpones, the initial stable growth angle. Our findings reveal that a developmental time window enables transient sensory dynamics to be translated into stable initial root growth angles, illustrating how developmental timing can convert short-lived signals into lasting form.