ISOLATION OF CHALCONE SYNTHASE AND CHALCONE ISOMERASE CDNAS FROM ALFALFA (MEDICAGO-SATIVA L) - HIGHEST TRANSCRIPT LEVELS OCCUR IN YOUNG ROOTS AND ROOT-TIPS

Flavonoids are involved in several different interactions between plan ts and microorganisms. In the Rhizobium-legume symbiosis, they play an important role as inducers of rhizobial nodulation (nod) genes. We ha ve identified from an alfalfa cDNA library four clones for chalcone sy nthase (CHS) and two clones for chalcone isomerase (CHI); CHS and CHI are key enzymes in flavonoid biosynthesis. In Medicago sp., CHS is enc oded by 8-12 genes, and CHI is encoded by 1-2 genes. Here we report th e DNA sequence of these clones as well as their relatedness to other l egume CHS and CHI clones. In addition, we report on the expression pat terns of two CHS gene family members as well as the CHI gene in M. sat iva cv. Iroquois. While CHS and CHI transcript levels are high in root tips and entire young roots, they are low in effective nodules elicit ed by wild-type strains of Rhizobium meliloti and very low in aerial p ortions of the plant (stems, leaves, flowers). However, wounding the c otyledons results in a rapid increase in transcript levels of both cha lcone synthase and chalcone isomerase genes in these organs.