Crop yield is majorly determined by the size of seeds, and studies are being conducted to understand the complex molecular network controlling the seed size. In this purview, Li et al. have explained the possible molecular mechanisms and regulatory networks underlying seed size control and growth. The review describes the factors regulating seed size by maternal and zygotic tissues. Several components of the ubiquitin-proteasome pathway including ubiquitin receptor, E3 ligase, ubiquitin-specific protease and deubiquitinating enzyme regulate seed size control in the model as well as non-model crop species. In rice and Arabidopsis, G-proteins have significant roles in seed size control. The OsMKKK10-OsMKK4-OsMAPK6 module promoting cell proliferation in spikelet hulls underlines the involvement of mitogen-activated protein kinases in controlling the grain size. The HAIKU (IKU) pathway and several phytohormones regulate the seed size by influencing endosperm development. However, studies on the role of embryo in determining seed size and the factors controlling embryo development are limited. Currently, delineating the upstream and downstream components of known seed size regulators and their interplay is necessary to understand the complete circuitry governing seed/grain size. Given that the mechanisms of seed size control are largely conserved, the research shall now focus on translating the knowledge generated in model plants to improve seed size in cultivated crops. (Summary by Muthamilarasan Mehanathan) Annu Rev Plant Biol 10.1146/annurev-arplant-050718-095851

Molecular Networks of Seed Size Control in Plants