UMAMIT44 exports plastidial glutamate and is essential for plant growth

Amino acids (AA) are fundamental components of peptides, proteins, and enzymes that play a critical role in plant growth, cellular metabolism, and stress response. Plants synthesize most AA within chloroplasts and require membrane transporters to transfer them from stroma to cytosol. Cytosolic AA are essential for synthesizing proteins and provide nitrogen support for the growth of sink organs, such as seeds. However, there are unknown players in plant chloroplasts involved in AA export. In new work by The et al., USUALLY MULTIPLE ACIDS MOVE IN AND OUT TRANSPORTER 44 (UMAMIT44) in Arabidopsis thaliana was discovered and shown to function as an AA exporter from chloroplasts. UMAMIT44 was identified as a candidate for plastidial export based on localization prediction tools and microscopy imaging, which showed that UMAMIT44 is localized in plastids throughout the plant but more abundant in green tissues. Physiological, biochemical, and molecular analyses of umamit44 mutants confirmed that it regulates glutamate export from plastids and maintains glutamate homeostasis within and outside chloroplasts. It was also seen to alter the source-to-sink transport of nitrogen, cellular redox state, and carbon metabolites, leading to adverse effects on plant growth and development. Overall, this study established UMAMIT44 as a key player in glutamate export from chloroplasts. (Summary by Maneesh Lingwan @LingwanManeesh) Plant Cell 10.1093/plcell/koad310