Ph.D., 1961,
Kansas State University
Professor
Center for
Agricultural Biotechnology
Plant Sciences
Building
University
of Maryland
College Park,
MD 20742
E-Mail: sd38@umail.umd.edu
Phone: (301)-405-1583
Research:
Plant protection; UV-B; flavonoids; soybean chalcone synthase gene family.
http://www.umbi.umd.edu/~cbr/dube.html
Environmental stresses (UV-B, temperature, drought, flood, salt, etc.) are among the major factors
in plant productivity losses in natural and agricultural conditions. Adding to the magnitude of this
problem is the accumulating evidence of increases in trace gases in the atmosphere, projecting global
shifts in the distribution of temperature and precipitation patterns, and increases in UV-B reaching
the earth. Since the stresses themselves are not readily controllable, enhancing plant productivity by
engineering improved protection mechanisms seems a more hopeful avenue.
Three categories of mechanisms are important in protection from UV-B damage: attenuation of
UV-B by flavonoids, photorepair of damaged DNA, and transcriptional regulation of certain genes
specifically responsive to UV-B. The enzyme catalyzing the formation of the central intermediate in
flavonoid biosynthesis pathway is chalcone synthase (CHS). We have cloned, sequenced, and
characterized the CHS gene family in soybean, a crop of major importance in the U.S. agricultural
economy and particularly prone to productivity losses from supplemental UV-B. Our work has
shown that this gene family consists of at least seven members, one inducible by broad spectrum light
as well as UV-B, another only by UV-B, yet another by sucrose and two genes in a bidirectional
promoter linkage, differing in their light responsiveness. Our results showing chs transcripts in
two-day dark-grown seedlings, when the inducibility by light and regulation by UV-B are barely
detectable, point to the importance of flavonoids already early in plant life, when the seedlings are
under the ground and the constitutive expression of chs genes must provide the means for their
biosynthesis. Our results have further shown that the photoregulation became much stronger in
three-day dark-grown seedlings, nicely coinciding with the time when stem elongation of seedlings
became most prominent, as if to prepare young plants for protection from environmental light
exposure just in time when the head is pushed up above the ground, suggesting the existence of a
fine-tuned developmental switch. The importance of flavonoids in UV-B protection is further
suggested by the finding that the UV-B-sensitive soybean cultivar, CNS, is more susceptible to
photodegradation of D1-D2 PSII reaction center heterodimer than the UV-B-resistant cultivar,
Williams. Further work on dissecting promoter elements in regulation of flavonoid biosynthesis, on
determining the relative contribution of photorepair in soybean cultivars of contrasting UV-B
sensitivities, and on identifying genes whose expression is regulated by UV-B, is in progress.
DNA sequences deposited in the GenBank database:
Genomic clones:
Rice 4-Coumarate:CoA Ligase 1, Os 4-cl.1 (X52623)
Soybean Chalcone Synthase 1, Gm chs1 (X54644)
Soybean Chalcone Synthase 2, Gm chs2 (X65636)
Soybean Chalcone Synthase 3, Gm chs3 (X53958)
Soybean Chalcone Synthase 4, Gm chs4 (X52097)
Soybean Chalcone Synthase 5, Gm chs5 (L07647)
Soybean Chalcone Synthase 6, Gm chs6 (L03352)
Soybean Chalcone Synthase 7, Gm chs7 (M98871)
Soybean Chalcone Synthase 1-3, intergenic (X56749)
Sorghum XbaI Repetitive DNA, Sha XSR3 (X54624)
Sorghum XbaI Repetitive DNA, Sha XSR6 (X54625)
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2-A (X58910)
cDNA clones:
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2 23-A (X58909)
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2 23-B (X62426)
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2 23-BA(X62425)
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2 23-F (X55354)
Tobacco PSII Oxygen-Evolving Enhancer protein 2, Nt oee2 23-FA(X62427)
Soybean 1-Aminocyclopropane-1-Carboxylate Synthase, Gm acs1 (X67100)
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