Differential expression of rice Nramp genes in response to pathogen infection, defense signal molecules and metal ions

The Nramp genes encode a class of metal transporters that universally exist in both eukaryotes and prokaryotes. In animals such as the mouse, the Nramp1 gene is important for natural host resistance to the infection of intracellular pathogens. To investigate the potential role of Nramp genes in plant defense response, we have conducted expression analysis of three OsNramp genes in rice seedlings and cell suspension cultures. In 2-week-old rice seedlings, the expression of OsNramp1 appeared to be suppressed by Burkholderia glumae during the susceptible interaction, unaffected by a virulent Magnaporthe grisea isolate, but was significantly induced by an avirulent M. grisea isolate during the resistant interaction. The expression of OsNramp2 and OsNramp3 was also significantly induced by B. glumae and M. grisea, but their induction by the M. grisea isolate was weak during the susceptible interaction. In rice leaf tissues, OsNranip1 transcription was delayed and suppressed by jasmonic acid (JA) and abscisic acid (ABA), respectively, while OsNramp2 was induced by JA, ABA and ethephon. In rice suspension cells, OsNramp3 was activated by the M. grisea cell wall elicitor and ABA. The elicitor-stimulated OsNramp3 expression was Ca2+ dependent and could be accentuated by cycloheximide (CHX). Both OsNramp1 and OsNramp2 had relatively high basal expression in suspension cells, and their expression was not significantly affected by the defense signal molecules. However, OsNramp1 transcript was increased drastically with EDTA, while OsNramp1 and OsNramp2 were slightly suppressed by 10 mM ferrous iron. In contrast, OsNramp3 was induced by 10 mM ferrous iron and zinc. These results indicate that rice Nramp genes are differentially expressed in response to pathogen infection, defense signals and metal ions, and are potentially involved in plant defense response. (c) 2005 Elsevier Ltd. All rights reserved.