Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2006
Publication Date: 7/7/2006
Citation: Narayanan, N.N., Vasconcelos, M.W., Grusak, M.A. 2006. Expression profiling of Oryza sativa metal homeostasis genes in different rice cultivars using cDNA macroarrays. In: Proceedings of the Thirteenth International Symposium on Iron Nutrition and Interactions in Plants, July 3-7, 2006, Montpellier, France. p. 90.
Technical Abstract: Rice (Oryza sativa) has shaped the cultures, diets and economies of billions of people; unfortunately, rice is a poor source of many essential micronutrients and vitamins. Deficiencies in these micronutrients are common in developing countries, especially where rice is the staple food. In order to increase the metal ion content of plant foods, a very clear molecular understanding of metal homeostasis, involving knowledge of the basic physiological processes of metal absorption, distribution, and storage in plants is essential. To study this in rice, clones of 37 metal-related genes, including ZIPs, NRAMPs, and YSLs (coding for known or potential metal transporters), as well as NAS, FER, NAAT, FDH, GSTU, and PDR (involved in metal homeostasis), were obtained from the Rice Genome Resource Center (Japan). In rice, flag leaves are the major source of photoassimilates and metals at the time of seed fill; therefore, we analyzed the expression of these metal related genes in flag and non-flag leaves of four different rice cultivars exhibiting high and low seed mineral levels using cDNA macroarray technology. Validation of the macroarrays and reproducibility of the spots between replicate experiments were assessed, and results showed that replicates have the same intensity and are highly reproducible. Most of the genes were expressed at low levels, while 13 of them (OsIRT1, OsZIP1, OsZIP5, OsZIP7, OsZIP8, OsYSL3, OsYSL4, OsYSL5, OsYSL8, OsYSL9, OsNRAMP2, OsNRAMP4 and OsNRAMP7) were found to be highly expressed in both flag and non-flag leaves. No significant differences in expression levels between flag and non-flag leaves were found amongst the cultivars examined. We selected a subset of genes (one per gene family) that were highly induced in all the cultivars for further expression analysis using semi-quantitative PCR and real-time PCR; data will be presented. We also performed elemental analysis on the flag leaves and the non-flag leaves using inductively coupled plasma-optical emission spectroscopy and found that iron concentrations were higher in IR68144 compared to the other three genotypes in the flag and non-flag leaves: Cocodrie and IR58 being low and Taipei 309 being intermediate. Zinc levels in these plants were not significantly different between the flag and non-flag leaves. Functional analyses of selected gene products, using yeast complementation studies in order to verify their transport capacities and probable role in whole-plant metal nutrition, are in progress. Our results will be discussed with reference to the overall regulation of metal homeostasis genes and their potential involvement in the process of iron and zinc accumulation in rice grains. This work was supported in part by funds from USDA-ARS under Agreement No. 58-6250-6-001 and from the Harvest Plus Project under Agreement No. 58-6250-4-F029 to MAG.