UC San Diego

Nitrogen is a critical nutrient that has important functions in plants. It supports DNA and protein synthesis and serves as an important signal that regulates biochemical pathways and gene expression. Nitrate is the form most often used by plants and is often provided as a fertilizer; however, excess fertilizer application has lead to significant damage to the environment. The elucidation of nitrate metabolism and regulation has thus been an important endeavor that could help to reduce fertilizer use and improve the health of the environment. During the second step of nitrate assimilation, nitrate is converted to nitrite. While nitrate is a nutrient to plants, nitrite is toxic to plants upon accumulation. Yet, it has been previously shown that many nitrate-inducible genes also respond to nitrite. Recently, the Crawford lab identified three specific nitrate enhancer elements that are present within the NIA1 nitrate reductase promoter. In this work, these nitrate enhancer elements were found to mediate nitrite induction. A screen for nitrate enhancer elements within the NiR promoter was also performed. The sequence between Taq1 to RsaI in the NiR promoter is important for nitrate induction, and the sequence just downstream of the start of translation (to the Xho site) is important for high constitutive expression. The work presented here shows that nitrite responses in plants can be mediated by the same DNA enhancer elements that serve as nitrate elements, and may provide new tools for the search for new nitrate enhancer elements