ALUMINUM TOLERANCE IN TOBACCO PLANTS TRANSFORMED WITH A PLANT AND A BACTERIAL CITRATE SYNTHASE GENES REGULATED BY ROOT SPECIFIC AND CONSTITUTIVE PROMOTERS.

¹ EMBRAPA/CNPMS Rodovia MG 424 - Km 65 Sete Lagoas - Minas Gerais Brazil 35701-970

² University of Arizona Forbes Building Room 306 P.O.Box 210036 Tucson, Arizona, USA 85721-0036

³ EPAMIG Fazenda Experimental de Caldas - FECD Av. Santa Cruz, 500 Caixa Postal 33 Caldas - Minas Gerais - Brazil 37780-000

Aluminum (Al) toxicity severely inhibits plant growth in acid soils. One mechanism used by plants to cope with this problem is root exudation of Al-chelating organic acids to the rhizosphere. The objective of this work was to compare the Al tolerance of tobacco plants harboring constructs of Daucus carota and Escherichia coli's citrate syntethase (CS) coding sequences under constitutive CAMV35S and root specific promoters. The complete Daucus carota CS (AC) coding sequence was isolated by RT-PCR from leaf mRNA using primers designed based on published sequences. The same gene without the mitocondrial signal peptide (AD) was isolated by the same method. The E. coli CS coding sequence was isolated by PCR using genomic DNA. The CAMV35S promoter was isolated from the pCAMBIA binary vector by PCR using primers designed according to published sequences. The root specific promoter ToRB7 (S45406) was isolated from tobacco genomic DNA by PCR using the same strategy. Different combinations of genes and promoters were cloned into the binary vector pCAMBIA C2 1303 and used to transform tobacco mediated by Agrobacterium. Transformed tobacco plants have been compared with a step gradient selective media with variable Al concentrations. Visual comparisons are indicating that transgenic tobacco plants transformed with the Daucus carota CS gene under the control of a root specific promoter have more biomass than plants transformed with the same gene under control of the constitutive promoter CAMV35S in the absence of Al. Transgenic plants carring these constructs behaved differently in an Al step gradient agar media.