Precise tiller angle control by manipulating <i>TAC1</i> expression in rice

Tiller angle shapes plant architecture, and is one of the top traits in plant breeding. A compact plant type reduces shading between plants, especially at high planting density, but also creates a humid microenvironment often associated with a higher incidence of pathogen and pest attacks, especially under highly humid climates. However, how to precisely manipulate the tiller angle to achieve a desirable plant type has been under-approached. Here we report the creation of gradient tiller angles in indica rice by fine tuning the expression of TILLER ANGLE CONTROL1 (TAC1), a domesticated gene in cultivated rice. We edited the regions upstream and downstream of the TAC1 coding sequence using multiplex CRISPR-Cas9 technology and developed homozygous allelic lines carrying deletions/inversions of various sizes at different positions. Those lines displayed smooth gradient changes in tiller angle that aligned well with TAC1 expression levels. Additionally, changes in the TAC1 expression level had no impact on other agronomic traits examined. TAC1 is well conserved across species, including perennial fruit trees in which mutation of TAC1 orthologs leads to a broomy plant type. Thus, our results provide a guide to creating tiller angles for selection according to climate zones in rice breeding programs, this approach can be extended to diverse species for improving plant architecture.