Enzymatic and Molecular Characterization of Arabidopsis ppGpp Pyrophosphohydrolase, AtNUDX26

Abstract

Not only in bacteria but also in plant cells, guanosine-3′,5′-tetraphosphate (ppGpp) is an important signaling molecule, that affects various cellular processes. In this study, we identified nucleoside diphosphates linked to some moiety X (Nudix) hydrolases, AtNUDX11, 15, 25, and 26, having ppGpp pyrophosphohydrolase activity from Arabidopsis plants. Among these, AtNUDX26 localized in chloroplasts had the highest V_max and k_cat values, leading to high catalytic efficiency, k_cat/K_m. The activity of AtNUDX26 required Mg²⁺ or Mn²⁺ ions as cofactor and was optimal at pH 9.0 and 50 °C. The expression of AtNUDX26 and of ppGpp metabolism-associated genes was regulated by various types of stress, suggesting that AtNUDX26 regulates cellular ppGpp levels in response to stress and impacts gene expression in chloroplasts. This is the first report on the molecular properties of ppGpp pyrophosphohydrolases in plants.