Differential modification of flavonoid and isoflavonoid biosynthesis with an antisense chalcone synthase construct in transgenic Lotus corniculatus.

Three clonal genotypes of Lotus corniculatus L. (bird's foot trefoil) were transformed with an antisense chalcone synthase (CHS) gene construct made using a stress induced CHS17 cDNA from Phaseolus vulgaris under the control of the constitutive CaMV 35S promoter and Nos terminator via Agrobacterium rhizogenes. After initial screening, ten antisense and five control co-transformation events from each recipient clonal genotype were analysed. After elicitation with glutathione, the level of tannin accumulation was found to be increased in a number of antisense root cultures derived from the low (S33) and moderate (S50) tannin recipient genotypes. Six antisense and four control transformed lines from genotype S50 were selected for more detailed study. The antisense CHS construct was found to be integrated into the genome, with a copy number ranging from 1 to 5 and antisense orientation was confirmed by PCR. In transformed root cultures, increased CHS transcript levels were noted in a number of antisense lines. Biochemical analyses of glutathione-elicited-root cultures indicated a significant increase in tannin accumulation in antisense CHS lines and mean vestitol levels were reduced. These results show that the introduction of a heterologous antisense chalcone synthase construct into L. corniculatus resulted in an unpredicted molecular and biochemical phenotype. Such findings are discussed in relation to manipulation of this complex multigene family.