ACR11 promotes nitrogen assimilation and protein productivity during urea cultivation in duckweed Lemna minor

Nitrogen assimilation plays a crucial role in plant growth and protein accumulation. Urea is a widely used and low-cost nitrogen source; therefore, efficient assimilation of urea-derived nitrogen is critical for biomass accumulation and protein production in plants. However, the regulatory factors that enhance this process remain poorly understood. Here, we identify the chloroplast-localized ACT DOMAIN REPEAT 11 (ACR11) as a positive regulator of nitrogen assimilation in duckweed. Overexpression of LpACR11 increased growth rate, protein content and protein productivity of duckweed Lemna minor ZH0403 under urea nutrition, whereas RNAi-mediated knockdown caused opposite effects. Heterologous expression of LpACR11 in tobacco and rice also enhanced biomass and protein accumulation under urea cultivation conditions. Biochemical and metabolic analyses showed that LpACR11 overexpression was associated with increased Fd-GOGAT (ferredoxin-dependent glutamate synthase) activity, elevated glutamate accumulation, reduced ammonium accumulation and increased total amino acid content. Glutamate treatment further promoted GS2 (plastid glutamine synthetase) expression and activity, supporting a working model in which ACR11-associated enhancement of Fd-GOGAT activity increases glutamate accumulation and thereby promotes GS2-associated nitrogen assimilation. Together, these results indicate that ACR11 enhances chloroplast nitrogen-assimilation capacity and protein productivity during urea cultivation, providing a potential genetic target for improving protein productivity in duckweed and other crops.