S. Ananvoranich et al., CLONING AND REGULATION OF FLAVONOL 3-SULFOTRANSFERASE IN CELL-SUSPENSION CULTURES OF FLAVERIA-BIDENTIS, Plant physiology, 106(2), 1994, pp. 485-491
Flaveria spp. accumulate flavonol sulfate esters whose biosynthesis is
catalyzed by a number of position-specific flavonol sulfotransferases
. Although the accumulation of sulfated flavonols appears to be tissue
specific and developmentally regulated and to vary among related spec
ies, little is known about the mechanism of regulation controlling the
synthesis of these metabolites. In the present work, we report the is
olation of a cDNA clone from Flaveria bidentis (pBFST3) encoding flavo
nol 3-sulfotransferase (FS-ST), which catalyzes the first step in the
biosynthesis of flavonol polysulfates. This clone (pBFST3) was express
ed in Escherichia coli and produced an F3-ST with high affinity for th
e flavonol aglycones, quercetin, and its 7-methyl derivative, rhamneti
n. In addition, the synthetic auxin 2,4-dichlorophenoxyacetic acid was
shown to induce F3-ST enzyme activity and FS-ST mRNA transcript level
s in cell cultures of F. bidentis. The F3-ST mRNA levels increased wit
hin the first 3 h, reaching a maximum after 24 h of treatment, and rem
ained elevated for up to 48 h. Treatments with either quercetin 3-sulf
ate or quercetin 3,7,4'-trisulfate reduced F3-ST enzyme activity in ce
ll cultures but had no effect an the transcript levels. These results
are discussed in relation to the putative role of flavonoid conjugates
in the regulation of auxin transport.