Plants have no nervous system or brain.  What they learn
from “past experience” will be used via epigenetics factors.

What is said in this section applies to the animal kingdom,
but to a lesser extent.

There are three epigenetics factors that can have an impact
on genes functions.  These factors apply to plants as well as
animals.  But as pointed out, there a heavy reliance in the plant
world on epigenetics changes, they are used to react to the
outside world.  This discussion will therefore largely focus on
plants.  What then are these three epigenetics factors and what
role does each play?

Chromatin Structure – How DNA is Packed

If you were to write a text on a piece of paper, and then
proceed to fold the paper to make various origami shapes, every
time you unfold the paper to make the next shape, you will note
that, of course, the writing itself has not changed.  You can
amuse yourself for hours this way, at the end the information
written on the paper remains the same.

This analogy can be extended to DNA; it is packed together
into different chromatin structures, however, the genes remain
the same.  But there is an important difference.  The resulting
structure of the chromatin can affect the behavior of the genes.

For instance, the response of the plant to long periods of
cold depends on chromatin structure.  This is important in
agriculture since the crop’s response to cold often determines
when it will flower and what the yield will be.

Chromatin structure can be influenced by:

• The outside environment:  How cold or hot it is, the
  number of daylight hours, water availability, etc.;
• developmental stage:  Is the plant just a seedling or is
  it flowering;
• small RNAs.

When the cell divides, chromatin structure can be passed
from the parent cell to the daughter cell, but it is often reset
in the offspring of the plant.

DNA Methylation – When and How Much Genes Turn Off

Although every cell in the plant has the complete genome,
only certain genes are expressed in certain cells.  The genes
that are activated in the organism’s leaves are different than
the ones that are expressed in the plant’s roots.

DNA methylation is one of the processes that can permanently
turn off genes for the life of the plant.

In plants, flowering occurs early when there are low levels
of DNA methylation.  Why is that is not clear; research is
undertaken to determine what role DNA methylation plays in this
process.

In animals, it has been observed that DNA methylation turns
off cancer suppressing genes.  Scientists are now attempting to
use this understanding of DNA methylation to develop a test for
prostate cancer.

Researching DNA methylation, and other basic biological
processes like flowering, will improve our understanding of these
mechanisms and will hopefully lead to discoveries that could
improve plant health and yield.

Problems with DNA methylation can change behavior and in
turn can result in disease or developmental disorders.  For
instance, plants with abnormally low levels of DNA methylation
can have abnormal changes to their seed size and fertility.

Small RNAs

As outlined in section IV, RNA synthesizes proteins based on
instructions passed on from the DNA.  But small RNAs do not
manufacture proteins, instead, they have the following functions:

• Changing the chromatin structure.
• Interfering with the ability of other RNA to make protein,
  in other words turning off genes.
• Directing DNA methylation.
• Controlling various development stages.
• Providing virus protection.

“Hairpin RNAi” gene silencing technology produces certain
small RNAs that can silence genes.  This process has broad
application in plants to discover genes, turn off unwanted genes,
and to protect plants against viruses.  It has already been used
to make healthier oils in oilseed plants and to help develop a
blue rose.

As well, Hairpin RNAi can be used to identify useful genes
in animals, and determine the structure of virus and parasite
genes in order to develop precise drugs to cure the illnesses
they cause.

Source

CSIRO Plant Industry
Canberra, Australia
Epigenetics General Information
Inheritance… more than just genes
www.pi.csiro.au/markoliphant–
conf/oliphant_epigenetics_info.htm#epigenetics

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