MOLECULAR CHARACTERIZATION AND EXPRESSION OF ALFALFA (MEDICAGO-SATIVAL) FLAVANONE-3-HYDROXYLASE AND DIHYDROFLAVONOL-4-REDUCTASE ENCODING GENES

Flavonoids are plant phenolic compounds involved in leguminous plant-m icrobe interactions. Genes implied in the central branch (chalcone syn thase (CHS), chalcone isomerase (CHI)) or in the isoflavonoid branch o f the flavonoid biosynthesis pathway have been characterized in Medica go sativa. No information is available to date, however, on genes whos e products are involved in the synthesis of other types of flavonoids. In this paper we present the genomic organization as well as the nucl eotide sequence of one flavanone-3-hydroxylase (F3H) encoding gene of M. sativa, containing two introns and exhibiting 82-89% similarity at the amino acid level to other F3H proteins. This is the first report o n the genomic organization of a f3h gene so far. We present also the s equence of a partial dihydroflavonol-4-reductase (DFR) M. sativa cDNA clone. Southern blot experiments indicated that f3h and dfr genes are each represented by a single gene within the tetraploid genome of M. s ativa. By a combination of Northern blot and RT-PCR analysis, we showe d that both f3h and dfr genes are expressed in flowers, nodules and ro ots, with a pattern distinct from chs expression. Finally, we show tha t dfr is expressed in M. sativa leaves whereas f3h is not. The role pl ayed by these two genes in organs other than flowers remains to be det ermined.