Gravity-Sensing Tissues for Gravitropism Are Required for Anti-Gravitropic Phenotypes of lzy Multiple Mutants in Arabidopsis

Plant posture is controlled by various environmental cues, such as light, temperature, and gravity. The overall architecture is determined by the growth angles of lateral organs, such as roots and branches. The branch growth angle affected by gravity is known as the gravitropic setpoint angle (GSA), and it has been proposed that the GSA is determined by balancing two opposing growth components: gravitropism and anti-gravitropic offset (AGO). The molecular mechanisms underlying gravitropism have been studied extensively, but little is known about the nature of the AGO. Recent studies reported the importance ofLAZY1-LIKE(LZY) family genes in the signaling process for gravitropism, such that loss-of-function mutants ofLZYfamily genes resulted in reversed gravitropism, which we term it here as the anti-gravitropic phenotype. We assume that this peculiar phenotype manifests as the AGO due to the loss of gravitropism, we characterized the anti-gravitropic phenotype ofArabidopsislzymultiple mutant genetically and physiologically. Our genetic interaction analyses strongly suggested that gravity-sensing cells are required for the anti-gravitropic phenotype in roots and lateral branches. We also show that starch-filled amyloplasts play a significant role in the anti-gravitropic phenotype, especially in the root of thelzymultiple mutant.