GS11 encodes a microtubule-associated protein that modulates grain shape in rice

Grain shape is a key agronomic trait for grain yield and quality in crops. Studies on rice have revealed several complex signaling pathways governing cell proliferation and cell expansion during grain development. Although cell division is critical for these events, the mechanistic integration of cell division into these developmental processes to determine grain shape remains unclear. In this study, we have identified Grain Shape 11 (GS11) as a positive regulator of rice grain shape. Loss of GS11 function leads to mispositioning of the preprophase band (PPB), a cortical ring composed of microtubules and actin filaments that defines cell division orientation. This misregulation results in asymmetric divisions, reduced cell size, increased cell number, and disorganized cell arrangements, ultimately producing shorter and wider grains. GS11 encodes a plant-unique protein that associates with microtubules. GS11 physically interacts with OsTON1a and OsTON2, the components of TON1-TRM-PP2A (TTP) complex, to co-regulate PPB positioning and cell division orientation during mitosis. Moreover, GS11 genetically interacts with GW7 in regulating grain shape. Altogether, our results identify GS11 as a TTP-associated protein that functions in coordinating cell proliferation and expansion likely by modulating microtubule organization and PPB positioning, providing insights into rice grain shape regulation.