Functional analysis of iron-deficiency responsive cis-acting elements IDE1 and IDE2 in rice plants

Abstract

We have previously identified the novel cis-acting elements IDE1 (iron-deficiency-responsive element 1) and IDE2 through promoter analysis of barley iron-deficiency-inducible IDS2 gene using transgenic tobacco system. To analyze the function of IDE1 and IDE2 in rice plants, IDS2 promoter fragments containing IDE1 and IDE2 were introduced into rice. A fragment containing one copy each of IDE1 and IDE2 was shown to be sufficient to confer strong iron-deficiency-inducible expression in rice roots and leaves. The expression was dominant in vascular bundles and root exodermis, resembling the expression pattern of other rice genes related to iron acquisition via mugineic acid family phytosiderophores (MAs). Rice iron-deficiency-inducible genes detected by microarray analysis included genes involved in every biosynthetic step of MAs. Promoters of those genes possessed sequences homologous to IDE1 and/or IDE2 at high frequency, suggesting coordinately regulated expression of Graminaceous genes related to iron acquisition.