The froh gene family from Arabidopsis thaliana: Putative iron-chelate reductases

Abstract

A group of b-type cytochromes play central roles in both the uptake of iron by yeast, exemplified by the products of the FRE1 and FRP1 genes, and in pathogen defence by animals, exemplified by gp91phox from humans. There has been speculation that related proteins have similar roles in plants. We have recently isolated a family of genes from Arabidopsis thaliana, designated froh, which encode deduced proteins which fall into the same class as FRE1, FRP1 and gp91phox. This paper reports that root surface iron-chelate reductase activity was 2.7-fold greater in A. thaliana plants grown in 5 µM, relative to plants grown in the presence of 25 µM, Fe(III) EDDHA. Reversed transcriptase (RT) polymerase chain reactions (PCR) using RNA isolated from these plants detected increased accumulation of frohC transcripts in low iron. Products were RT-dependent and their identity confirmed by subsequent hybridisation to 32P-frohC probe and by sequence determination. The frohC transcripts accumulated in response to low iron in both roots and leaves while actin transcripts (control) remained constant. Exposure of leaves to salicylic acid (a potentiator of pathogen defense responses) led to an accumulation of transcripts encoding a pathogenesis-related protein, pr-1, but not frohC or actin transcripts. These observations suggest that FrohC is more likely to be involved in iron-reduction, either for uptake from the soil or re-translocation within the plant, than in pathogen defence.