EXPRESSION OF THE YEAST FRE GENES IN TRANSGENIC TOBACCO

Two yeast genes, FRE1 and FRE2 (encoding Fe(III reductases) were place d under the control of the cauliflower mosaic virus 35S promoter and i ntroduced into tobacco (Nicotiana tabacum L.) via Agrobacterium tumefa ciens-mediated transformation. Homozygous lines containing FRE1, FRE2, or FRE1 plus FRE2 were generated. Northern-blot analyses revealed mRN A of two different sizes in FRE1 lines, whereas all FRE2 lines had mRN A only of the expected length. Fe(III) reduction, chlorophyll contents , and re levels were determined in transgenic and control plants under Fe-sufficient and Fe-deficient conditions. In a normal growth environ ment, the highest root Fe(III) reduction, 4-fold higher than in contro ls, occurred in the double transformant (FRE1 + FRE2). Elevated Fe(III ) reduction was also observed in all FRE2 and some FRE1 lines. The inc reased Fe(III) reduction occurred along the entire length of the roots and on shoot sections. FRE2 and double transformants were more tolera nt to re deficiency in hydroponic culture, as shown by higher chloroph yll and re concentrations in younger leaves, whereas FRE1 transformant s did not differ from the controls. Overall, the beneficial effects of FRE2 were consistent, suggesting that FRE2 may be used to improve Fe efficiency in crop plants.