Although it's been 1.6 billion years since humans
shared a common ancestor with, say,
Arabidopsis, we
still have in common many basic genes, processes,
and functions. Studies of basic plant biology have
drawn from these commonalities and have led to significant
advances in our approaches to disease and
medicine. Some discoveries originally made in plants
have turned out to be fundamental to understanding
human biology. For example, some of the most basic
aspects of biology, such as the existence of cells,
nuclei, genes, and viruses were all first discovered
in plants. Plants also produce a tremendous variety
of chemical compounds, many with medicinal value.
Drug Discovery
In ancient Greece and Rome, the bark of
the willow tree was widely used to treat
fever, aches, and labor pains. Ancient writings—
from as early as 3000 B.C.—make
it clear that people have been aware of
the tree's medicinal properties for a very
long time. Scientists isolated the potent
compound that gave the bark its healing
power in the early 1800s, naming it
salicylic acid (after
Salix, the Latin name
for willow). Salicylic acid continues to figure
prominently in medicines: today it is
used to treat acne, psoriasis, warts, and
diarrhea, among other ailments. It is also
well known for its key role in the production
of aspirin, which is simply a slightly
modified form of salicylic acid.
The site
(marked with a "T") where
the anti-cancer drug
taxol interacts
with tubulin proteins to prevent
cell
division. Image courtesy Lawrence
Berkeley National Laboratory.Although many medicinal plants have
been in use for thousands of years, new
ones are still being discovered. In the
1960s, the U.S. government embarked
on a project to screen plants for cancerfighting
compounds. Scientists identified
a promising compound in the bark
of the Pacific yew, a smallish evergreen
that grows in the Pacific Northwest. The
compound, which was named taxol, has
since been shown to disrupt cell division
and growth and has been used to treat
ovarian, breast, lung, head and neck, and
gastrointestinal tract cancers. Scientists
have also found a way to synthesize taxol
in the laboratory, greatly reducing the
need to harvest the Pacific Northwest's
ancient trees.
The Food and Agriculture Organization
of the United Nations estimates that
the active ingredients of 25 percent of
all prescription drugs come from plants.
Continued research is likely to unearth
even more. Genomic sciences will be critical
to isolating and manufacturing medically
useful plant-based products.
Immunity
and Mechanisms of Disease
Like humans, plants also get diseases—
and use their immune systems to respond.
Sometimes, the immune system
overreacts and exhibits responses with
deleterious effects. This is the case with
human autoimmune diseases, such as
Crohn's disease, a chronic inflammatory
bowel disease.
In the mid-1990s, scientists studying
plants identified proteins called NB-LRR
proteins, which are the key receptors of
plant immune systems and are used for
fighting disease. Scientists later identified
related genes in humans. These human
genes also code for proteins involved in
immunity and inflammatory responses,
and studying them has provided clues
about the mechanisms behind inflammatory
diseases. Similarities between the
plant NB-LRR disease resistance proteins
and these human genes also helped
a team of researchers identify the gene
responsible for Crohn's disease.
Small RNA and Plant
Defense
Artist's rendering of RNA. Image courtesy
of Nicole Rager
Fuller, National Science Foundation.Small RNA is a short molecule that packs
a big punch. Historically, it was believed
that RNA served merely as a messenger,
shuttling genetic instructions between
DNA and proteins. But thanks to plant
research, scientists now recognize the
diverse array of functions performed by
these small strands of RNA—measuring
just 18-24 nucleotides long.
What is a plant to do when an herbivore,
say, an insect, begins to eat it? The
answer, for some plants, is to call in the
troops—sending small RNAs to coordinate
defense responses, including regeneration
by the plant's stem cells. Recent
research even suggests that some small
RNAs can directly fight herbivorous insects
by silencing specific genes in the insect
when the plant is ingested.
Insights from plant research have
also expanded our understanding of the
functions of small RNAs in animals and
humans. Some small RNAs silence, or
suppress the expression of, certain genes.
This is known as RNA interference. Understanding
how RNA interference works
could lead to major medical advances.
Such diseases as Alzheimer's and arthritis
are triggered by the expression of genes.
Scientists are exploring ways to use RNA
interference to silence those genes, and
thus prevent those diseases.
This web page is based on the National Academies' educational booklet
New Horizons in Plant Sciences.
