Figure 9.

A proposed model for the role of the HDR3–GW6a module’s regulation of grain size (length) and weight in rice. HDR3 acts as an active ubiquitin receptor of UIM type and interacts with the positive grain-size regulator GW6a, leading to the enhanced GW6a ubiquitylation (K63-linked polyubiquitin chains) and delay of its degradation by the 26S proteasome, thereby boosting cell division and spikelet hull size, subsequently increasing milk filling rate and, ultimately, grain size (length) and weight