CHALCONE SYNTHASE GENE-EXPRESSION IN TRANSGENIC SUBTERRANEAN CLOVER CORRELATES WITH LOCALIZED ACCUMULATION OF FLAVONOIDS

Expression patterns of two clover chalcone synthase promoters (TsCHS1 and TsCHS3) were examined in transgenic Trifolium subterraneum plants to investigate flavonoid gene regulation and to determine if there is differential regulation of these promoters from the CHS multigene fami ly. The CHS1 and CHS3 genes occur as part of a tightly linked cluster of tandemly orientated genes in subterranean clover. The CHS promoters were fused to the beta-glucuronidase (GUS) reporter gene and reintrod uced into subterranean clovers. Analysis of the expression of the repo rter genes showed that near-identical expression patterns occurred in the transgenic plants containing either the CHS1:GUS or the CHS3:GUS f usions. Both promoters responded rapidly to wounding of the shoot. Dis tinct changes in the expression patterns of both promoters occurred du ring the development of leaves and flowers. In young shoots, expressio n occurred throughout the tissues and was restricted to the cambium an d xylem parenchyma in mature tissue. Roots possessed the highest activ ity levels, which were primarily located in the meristematic tissues o f the tap root, lateral root and nodule. Epifluorescent localisation o f flavonoids using diphenylboric acid-2-aminoethylester correlated wit h the site of GUS activity in most tissues. These results indicate tha t histochemical detection of CHS expression in various root meristems and flower parts is correlated with localised flavonoid accumulation i n these cells. Our studies suggest a physiological role for flavonoids at those sites.