The nitrogen response of a barley C-hordein promoter is controlled by positive and negative regulation of the GCN4 and endosperm box

The 431 bp C-hordein promoter of λ- 1 - 17 exhibits a specific response to amino acids and NH₄NO₃ in developing barley ( Hordeum vulgare L.) endosperms. With the aid of particle bombardment it is shown that the GCN4 motif ATGA(C/G)TCAT is the dominating cis -acting element in this response. But synergistic interaction with the neighbouring endosperm motif TGTAAAGT within the bifactorial prolamin element and cooperation with upstream sequences including a second prolamin-like element is an absolute requirement for a strong, positive regulation by an optimal nitrogen regime. Low nitrogen levels convert the GCN4 box into a negative motif. In contrast the endosperm box on its own exerted a silencing activity, independent of nitrogen nutrition. Sequence comparisons revealed that GCN4- and endosperm-like motifs are widely distributed among plant promoters. Their putative role in nitrogen regulation is discussed.