Rice flavonoid pathway genes, OsDfr and OsAns, are induced by dehydration, high salt and ABA, and contain stress responsive promoter elements that interact with the transcription activator, OsC1-MYB

Molecular basis of regulation of abiotic stress responses and the flavonoid biosynthesis in rice was investigated. The role of the regulatory gene OsCl-Myb, encoding a MYB class of transcription activators in the stress-induced expression of the structural genes, OsDfr and OsAns, was analyzed. Northern analysis of shoot tissues of rice, Nagina 22, (Oryza sativa L. sub sp. indica) seedlings under dehydration stress or high salt or abscisic acid (ABA) showed a significant enhancement of transcript level and/or transcript stability of Ospfr and OsAns. Enhanced levels of the OvCl-myb transcript were also detected. The expression pattern of these three genes indicates that the stress responsive accumulation of Ospfr and OsAns transcripts is mediated by the transcription factor, OsCl -MYB. The 5' upstream region of the OsDfr and OsAns genes carry several regulatory domains, which share homology with some of the known stress responsive genes in plants. In addition, several putative myb and myc responsive domains were identified in the promoter region of the genes, Ospfr and OsAns. The recombinant OsCl-MYB protein binds in vitro to the myb responsive elements (MREs) in the OsDfr and OsAns promoters, suggesting that it is a potential transcription activator of stress-induced expression of structural genes of the flavonoid pathway. (C) 2004 Elsevier Ireland Ltd. All rights reserved.