The Arabidopsis LAZY1 Family Plays a Key Role in Gravity Signaling within Statocytes and in Branch Angle Control of Roots and Shoots.

During gravitropism, the directional signal of gravity is perceived by gravity-sensing cells called statocytes, leading to asymmetric distribution of auxin in the responding organs. To identify the genes involved in gravity signaling in statocytes, we performed transcriptome analyses of statocyte-deficient mutants and found two candidates from the LAZY1 family, / () and // We showed that , , and a paralog are redundantly involved in gravitropism of the inflorescence stem, hypocotyl, and root. Mutations of genes affected early processes in gravity signal transduction without affecting amyloplast sedimentation. Statocyte-specific expression of genes rescued the mutant phenotype, suggesting that genes mediate gravity signaling in statocytes downstream of amyloplast displacement, leading to the generation of asymmetric auxin distribution in gravity-responding organs. We also found that mutations reversed the growth angle of lateral branches and roots. Moreover, expression of the conserved C-terminal region of LZY proteins also reversed the growth direction of primary roots in the mutant background. In lateral root tips of multiple mutants, asymmetric distribution of PIN3 and auxin response were reversed, suggesting that genes regulate the direction of polar auxin transport in response to gravity through the control of asymmetric PIN3 expression in the root cap columella.