ITHACA,
N.Y. (9/4/97)- One of the genes first studied by Gregor Mendel in his
famous experiments with pea plants has now been cloned by plant biologists.
The father of genetics, Gregor Mendel (1822-1884), worked in a
monastery more than 130 years ago, in what is now the Czech Republic. In
his famous experiments with peas, he selected seven distinct characteristics
of pea plants and followed their expression through several generations.
One of the traits he studied was stem length, the primary determinant of
plant height. A team of researchers from Cornell University and the
University of Tasmania, Australia, now report cloning the gene for stem
growth.
This accomplishment should provide new insight into plant physiology.
Cloning the gene will help explain height differences in otherwise similar
plants.
"This is one of the most important genes in history as it illustrates
the principles of genetics, said Peter Davies, Cornell professor of plant physiology, who worked
on this research during a recent sabbatical in Australia.
The plant scientists working at the University of Tasmania, Hobart,
Australia, isolated, cloned and obtained the DNA sequence of the pea plant's tallness gene,
and showed that it codes for gibberellin 3-beta-hydroxylase. This enzyme is crucial
to the division and elongation of the cells in the plant's stem.
The Tasmanian group demonstrated in 1984 that tallness in pea plants
is regulated by an acid called gibberellin, or GA1. Gibberellic acid had been discovered
in the 1950s, but it was not until the early 1980s that the group connected
it to stem height.
Now, the researchers have demonstrated that in the tall pea plants used
by Mendel, the tallness gene codes for an enzyme that adds a hydroxyl (HO) group at
a very particular location onto GA20, which is the is the immediate precursor of GA1.
In the dwarf plants there is a change of one base in the DNA sequence,
which leads to a change of one amino acid in the resulting protein. In turn, this results
in an enzyme that is still active in converting GA20 into GA1, but at 1/20th the rate. Therefore,
dwarf peas are less efficient at synthesizing the gibberellic acid responsible for promoting
stem growth. The plant becomes growth deficient, explained Davies.
Mendel's description of units of heredity, the formulation of the Laws
of Segregation and Independent Assortment, and his coining of the concepts
of dominant, recessive, and discrete factors -- later called genes -- remain
the foundations of genetics today. While Mendel first announced his findings
in 1865, they remained largely unnoticed until 1901 when they were translated
into English and presented in London and New York.
"Mendel's experiments are now included in every high school biology
class," said Davies.
The findings are reported in (Vol. 9, published August 26, 1997) of
The Plant Cell, the journal of the American Society of Plant Physiologists.
ITHACA,
N.Y. (9/4/97)- One of the genes first studied by Gregor Mendel in his
famous experiments with pea plants has now been cloned by plant biologists.
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