Genes controlling hydroxylations of phytosiderophores are located on different chromosomes in barley (Hordeum vulgate L.)

Phytosiderophores, mugineic acids, have been demonstrated to be involved in Fe acquisition in gramineous plants. In this study, chromosomal arm locations of genes encoding for biosynthesis of various phytosiderophores were identified in a cultivar of barley (Hordeum vulgare L. cv. Betzes). Using wheat (Triticum aestivum L. cv. Chinese Spring)-barley (cv. Betzes) ditelosomic addition lines for 4HS and 4HL, a gene for hydroxylation of 2'-deoxymugineic acid to mugineic acid was localized to the long arm of barley chromosome 4H. To locate the gene for hydroxylation of mugineic acid to 3-epihydroxymugineic acid, hybrids between the 4H addition line and other wheat-barley addition lines were studied. Only a hybrid between 4H and 7H addition lines produced 3-epihydroxymugineic acid. The gene was further localized to the long arm of chromosome 7H by feeding mugineic acid to ditelosomic addition lines for 7HS and 7HL. A new phytosiderophore was discovered in both 7H and 7HL addition lines, which was identified to be 3-epihydroxy-2'-deoxymugineic acid by detailed nuclear magnetic resonance studies. These results revealed that in barley there are two pathways from 2'-deoxymugineic acid to 3-epihydroxymugineic acid: 2'-deoxymugineic acid → mugineic acid → 3-epihydroxymugineic acid and 2'-deoxymugineic acid → 3-epihydroxy-2'-deoxymugineic acid → 3-epihydroxymugineic acid. Barley genes encoding for the hydroxylations of phytosiderophores are located in different chromosomes and each gene hydroxylates different C-positions: the long arm of chromosome 4H carries the gene for hydroxylating the C-2' position and the long arm of chromosome 7H carries the gene for hydroxylating the C-3 position of the azetidine ring.