IGT/LAZY family genes are differentially influenced by light signals and collectively required for light-induced changes to branch angle

Plants adjust their growth orientations in response to environmental signals such as light and gravity in order to optimize photosynthesis and access to nutrients. However, given the fixed nature of gravity, understanding how light and gravity signals are integrated is challenging. Branch orientation, or gravitropic set point angle, is a key aspect of plant architecture, set with respect to gravity and shown to be altered by changes in light conditions. The IGT gene family, also known as the LAZY family, contains important components for branch angle and gravity responses, including three gene clades: LAZY, DEEPER ROOTING (DRO), and TILLER ANGLE CONTROL (TAC). LAZY and DRO genes promote upward branch orientations downstream of amyloplast sedimentation, and upstream of auxin redistribution in response to gravity. In contrast, TAC1 promotes downward branch angles in response to photosynthetic signals. Here, we investigated the influence of different light signaling pathways on LAZY and DRO gene expression, and their role in light regulation of branch angle responses. We found differential effects of continuous light and dark, circadian clock, photoreceptor-mediated signaling, and photosynthetic signals on LAZY and DRO gene expression. Phenotypic analysis revealed that LAZY and DRO genes are collectively required for branch angle responses to light.