Characterization of promoter expression patterns of OsNrt2.1 , a nitrate transporter gene of rice ( Oryza sativa L.)

Abstract

Nitrate is one form of available nitrogen nutrient, and its uptake and transport in plants was mediated by nitrate transporters. It is important to elucidate the transcription mechanism of nitrate genes at the molecular level. In this study, the promoter of OsNrt2.1, a rice nitrate transporter gene previously cloned in our group, has been characterized. Based on PLACE online analysis, some important cis-regulatory elements were identified. Under the control of the full length fragment of OsNrt2.1 promoter (P-2047), the expression of the reporter gene Gus was up-regulated when exposed to low nitrogen. Promoter deletion analysis indicated that the low nitrate responding elements located at position −524 to −1 and −980 to −525. Several cis-regulatory elements such as CIACADIANLELHC and −10 promoter element, located at positions of −524 to −1, −980 to −525, −1487 to −981, and −2047 to −1488 in P-2047, were possibly involved in the circadian regulation of the OsNrt2.1 gene. Sugar signaling and sugar-responsive motif WBOXHVISO1 and TATCCAOSAMY were also identified in P-2047, suggesting that the exogenous sugar variations resulted from the photosynthesis changes were related to the up-regulated expression of Gus during the day time. It is guessed that the expression pattern of Gus with low-nitrate inducible and diurnal rhythm was partly, at least, via the mediation of Ca²⁺ signal transduction pathway. Owing to its regulation pattern with low nitrate inducible and typical circadian pattern, the OsNrt2.1 promoter maybe has a potential role in the generation of transgenic crop varieties with high-N use efficiency in the future.

Key words： rice (Oryza sativa L.); nitrate transporter gene; OsNrt2.1 promoter; cis-regulatory elements