D-amino acid aminotransferase1 regulates grain chalkiness in rice by modulating endoplasmic reticulum stress response.

Abstract

D-amino acids are key components of the bacterial cell wall and play important roles in neural communication and inflammatory responses in animals. However, knowledge about D-amino acid metabolism and physiological functions in plants is limited. Here, we isolated and characterized a rice <i>D-amino acid</i> <i>aminotransferase1</i>, <i>OsDAAT1</i>, which maternally regulates rice grain chalkiness through map-based cloning and a subsequent complementation test. We found that <i>OsDAAT1</i> is highly expressed in the vascular tissue of rice nodes and is capable of interconverting different D-amino acids in vitro. Mutation of <i>OsDAAT1</i> results in elevated D-alanine levels in stems, nodes, and developing grains. The disruption of D-amino acid metabolism subsequently leads to significantly altered peptide/protein isomerization, including some key enzymes involved in starch and protein biosynthesis. These changes trigger severe endoplasmic reticulum stress and ultimately leads to chalky grains. Furthermore, we identified <i>OsDAAT1^Hap1</i>as a low-chalkiness haplotype, and historical frequency analysis suggests that <i>OsDAAT1</i> may have undergone selection during rice domestication. Overall, our findings uncover a previously unrecognized role in D-amino acid metabolism in plants and facilitate the practical use of <i>OsDAAT1</i> in grain appearance quality improvement in rice.