Involved in the regulation of shoot gravitropism and tiller angle through negative regulation of basipetal polar auxin transport (PAT) (PubMed:17468779, PubMed:17412736, PubMed:25028496). Acts as positive regulator of lateral auxin transport (PubMed:17468779, PubMed:25028496, PubMed:17412736). Promotes vertical shoot growth (PubMed:17908158). LAZY1 and TAC1 play opposite functions in the regulation of tiller growth angle (PubMed:17908158). Expressed specifically in the cells at the inner side of the vascular bundles of young leaf sheaths and peripheral cylinders of vascular bundles in the unelongated stems (PubMed:17468779). Expressed in the leaf sheath pulvinus and the lamina joint (PubMed:17412736). Tiller-spreading phenotype due to defective shoot and tiller gravitropism. Extremely larger leaf angle at reproductive stage. Altered endogenous auxin distribution in shoots. Belongs to the LAZY family.