Arabidopsis TSO1 and MYB3R1 form a regulatory module to coordinate cell proliferation with differentiation in shoot and root

Significance

Plant postembryonic development relies on a small pool of stem cells at the shoot and root tip. The question of how the cell cycle regulatory activities are integrated into the specific stem cell context is not well understood. This study identifies a previously unknown regulatory module in the flowering plant consisting of two regulatory genes, TSO1 and MYB3R1. TSO1 negatively regulates MYB3R1 to control cell division activity, maintain proper stem cell pool size, and balance cell proliferation with differentiation in shoot and root. Significantly, animal homologs of TSO1 and MYB3R1 are members of a cell cycle regulatory complex, suggesting that this conserved module operates in both plants and animals.

Abstract

Fundamental to plant and animal development is the regulated balance between cell proliferation and differentiation, a process intimately tied to cell cycle regulation. In Arabidopsis, mutations in TSO1, whose animal homolog is LIN54, resulted in severe developmental abnormalities both in shoot and root, including shoot meristem fasciation and reduced root meristematic zone. The molecular mechanism that could explain the tso1 mutant phenotype is absent. Through a genetic screen, we identified 32 suppressors that map to the MYB3R1 gene, encoding a conserved cell cycle regulator. Further analysis indicates that TSO1 transcriptionally represses MYB3R1, and the ectopic MYB3R1 activity mediates the tso1 mutant phenotype. Since animal homologs of TSO1 and MYB3R1 are components of a cell cycle regulatory complex, the DREAM complex, we tested and showed that TSO1 and MYB3R1 coimmunoprecipitated in tobacco leaf cells. Our work reveals a conserved cell cycle regulatory module, consisting of TSO1 and MYB3R1, for proper plant development.