Submitted to: Soil Science and Plant Nutrition (SSPN)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2004
Publication Date: 12/20/2004
Citation: Vasconcelos, M., Musetti, V., Li, C., Datta, S.K., Grusak, M.A. 2004. Functional analysis of transgenic rice (Oryza sativa L.) transformed with an Arabidopsis thaliana ferric reductase (atfr02). Soil Science and Plant Nutrition. 50:151-1157. Interpretive Summary: Rice is one of the major food crops worldwide, and for many it is the main source of calories. Rice is a very diverse species, and it can be grown in many types of ecosystems such as irrigated, rain-fed lowland, upland, and flood prone soils. Although upland rice constitutes a relatively small proportion of the total rice area worldwide (around 13%), it is the predominant method of rice culture in Latin America and West Africa. For this culture method, there are sometimes problems of plant iron deficiency, due to low availability of iron in the soil. When this occurs, there often are lower yields, and reduced levels of iron in the harvested grains. In addition, part of the problem stems from the fact that rice is not very efficient at absorbing iron when the availability of iron in soils is low. As a means to deal with this problem, we have attempted to enhance the rice plant's ability to cope with iron deficient conditions by incorporating the gene from another plant into rice. This other plant's name is Arabidopsis. In theory, the Arabidopsis gene should enable the rice plant to make a protein in its roots that will modify the form of iron outside the plant, and this form should be more easily absorbed by the roots. The gene we introduced into rice included instructions for making this protein in Arabidopsis roots, and one thing we wanted to test was whether these instructions also would result in the protein being made in rice roots. Unfortunately, we discovered that these instructions did not work in rice, and thus we found no evidence for the protein in rice roots. It appears that alternative instructions are needed to produce this protein in rice, and until that can be achieved, we are unable to test whether this protein can assist rice in obtaining more iron.
Technical Abstract: Iron deficient soils limit crop production on 25-30% of the world's arable land. Both grasses (Strategy II) and dicotyledonous crops (Strategy I) are susceptible to iron deficiency, but each respond to iron stress by different mechanisms. In order to acquire iron from the soil, Strategy I plants utilize an iron reduction and Fe2+ transporter system at the root level, whereas Strategy II plants use a phytosiderophore-based system. Unfortunately, in some grasses such as rice, the production of phytosiderophores is low, and thus their ability to survive in iron-deficient conditions is limited. To determine whether a Strategy I root reductase can function in a Strategy II plant, and enhance its iron acquisition, we inserted the FRO2 gene from Arabidopsis thaliana (AtFRO2) into rice (Oryza sativa). Root reductase activity was determined and was found to be low in both transgenic and control plants grown at different iron concentrations. The low activity levels were attributed to the release of soluble reductants in the assay and not to membrane-localized root reductase activity. RT-PCR analysis of rice roots and shoots of plants grown hydroponically at different iron concentrations revealed no expression of the transgene. In this paper, we discuss the lack of functionality of the AtFRO2 gene in rice, and we perform a comparative study of the 0.6 kb promoter region by PlantCARE and PLACE analysis.