Molecular biologists from Tübingen have discovered how the growth of leaves
and the aging process of plants are coordinated
Plants that grow more slowly stay fresh longer. In their study now published
in PLoS Biology, scientists at the Max Planck Institute for Developmental
Biology in Tübingen have shown that certain small sections of genes,
so-called microRNAs, coordinate growth and aging processes in plants. These
microRNAs inhibit certain regulators, known as TCP transcription factors.
These transcription factors in turn influence the production of jasmonic
acid, a plant hormone. The higher the number of microRNAs present, the lower
the number of transcription factors that are active, and the smaller the
amount of jasmonic acid, which is produced by the plant. The plant therefore
ages more slowly, as this hormone is important for the plant?s aging
processes.

The researchers have succeeded for the first time in describing the
antagonistic regulation of growth and aging in plants. Since the quantity of
microRNAs in the plants can be controlled by genetic methods, it may be
possible in future to cultivate plants that live longer and grow faster.

MicroRNAs are short, single-strand sections of genes that regulate other
genes. They do this by binding to complementary sections of the genetic
material, thus preventing them from being read and implemented in genetic
products. In plants, microRNAs mainly inhibit other regulators, so-called
transcription factors. These factors can switch genes on or off by binding
to DNA sections, thus activating or blocking them so that either too many or
too few proteins are formed. Since proteins control metabolic processes, an
imbalance leads to more or less clearly visible changes to the plant.

The scientists in Prof. Detlef Weigel?s department at the Max Planck
Institute for Developmental Biology have investigated the effects that the
transcription factors of the TCP family have on the growth and aging of the
thale cress model plant (Arabidopsis thaliana). These transcription factors
are regulated by the microRNA miR319.

It was already known that miR319-regulated transcription factors affect the
growth of leaves. Using a combination of biochemical and genetic analyses,
the researchers have now discovered that the transcription factors also
regulate those genes that are essential for the formation of the plant
hormone jasmonic acid. The higher the amount of microRNA miR319 present in
the plant, the lower the number of transcription factors that are produced.
This results in smaller amounts of jasmonic acid which can be synthesized.
Plants containing little jasmonic acid age more slowly: The leaves become
yellow and the plant dies. This process can be stopped by treating the plant
with the hormone.

"Our studies show that the transcription factors, which are regulated by the
microRNA miR319, exert a negative influence on the growth of plants, and
also lead to premature aging. The mechanism discovered here is a further
milestone in the attempt to explain the relationships of genetic regulation
in plants. Only when we have a better understanding of these processes will
we be able to produce plants that have particularly desired properties,"
says Detlef Weigel, who heads the project.

About the Max Planck Institute
The Max Planck Institute for Developmental Biology conducts basic research
in the areas of biochemistry, genetics and evolutionary biology. It has some
325 employees and is located at the Max Planck campus in Tübingen, Germany.
The MPI for Developmental Biology is one of 82 Institutes and research labs
of the Max Planck Society for the Promotion of Science e.V.

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