every chimeric repressor exhibit high sterility. The ortholog gene of AP3 was used
in rice, known as Super Woman (SPW1), and it was silenced by obtaining a sterile
masculine phenotype with a high efficiency. These results indicate a powerful tool
for the control of fertility in monocots and dicots (Mitsuda et al. 2006).
15.6 Epigenetic Strategies for Pathway Modification
Gene expression driven by developmental and stress cues often depends on posttranslational modifications of histone and sometimes on DNA methylation. Most of
these stress-induced modifications are reset to the basal level once the stress is
relieved, while some of the modifications may be stable, that is, may be carried
forward as ‘‘stress memory’’ and may be inherited across mitotic or even meiotic
cell divisions (Chinnusamy and Zhu 2009; De Groote et al. 2012). Epigenetic stress
memory may help plants for confront of with subsequent stresses more effectively;
comparative studies on stress-responsive epigenomes and transcriptomes will
enhance our understanding of stress adaptation of plants. As sessile organisms,
plants need to continuously adjust their responses to external stimuli for changing
growth conditions (Zhang et al. 2012). Since the seed dispersal range is often rather
limited, exposure of progeny to the growth conditions of parents is very probable.
The plasticity of plant phenotypes cannot be simply explained by genetic changes
such as point mutations, deletions, insertions, and gross chromosomal rearrangements (Hauser et al. 2011). Since many environmental stresses persist in one or
several plant generations, other adaptation mechanisms must exist. The inheritability of reversible epigenetic modifications, that regulate gene expression without
changing DNA sequence, makes them an attractive alternative mechanism (Boyko
and Kovalchuk 2011). Despite significant advances made in epigenetic research in
recent decades, many questions remain unsolved, especially concerning gene
expression modulation (GEM). Epigenetic marks are enzyme-mediated chemical
modifications of DNA and its associated chromatin proteins. Although they do not
alter the primary sequence of DNA, they also contain inheritable information and
play key roles in regulating genome function. Such modifications including cytosine methylation, posttranslational modifications of histone tails and the histone
core, and the positioning of nucleosomes (histone octamers wrapped with DNA).
These constructs influence the transcriptional state and other functional aspects of
chromatin (Feng and Jacobsen 2011). Adverse environmental phenomena distort
the growth, development, and productivity of crop plants. As a defense, plants have
sophisticated mechanisms to respond and acclimatize to these stresses conditions
by prompt changes at transcriptional and posttranscriptional levels of whole gene
complexes. Various genes belonging to diverse transcription factor families have
been shown to regulate stress-responsive genes, thus playing an important role in
stress signaling. Recently, epigenetic mechanisms have been implicated in the
regulation of the expression of genes related to abiotic or biotic stresses
(Chinnusamy and Zhu 2009). These mechanisms regulate almost all the genetic
15 Plants as Bioreactors for Human Health Nutrients
439
in rice, known as Super Woman (SPW1), and it was silenced by obtaining a sterile
masculine phenotype with a high efficiency. These results indicate a powerful tool
for the control of fertility in monocots and dicots (Mitsuda et al. 2006).
15.6 Epigenetic Strategies for Pathway Modification
Gene expression driven by developmental and stress cues often depends on posttranslational modifications of histone and sometimes on DNA methylation. Most of
these stress-induced modifications are reset to the basal level once the stress is
relieved, while some of the modifications may be stable, that is, may be carried
forward as ‘‘stress memory’’ and may be inherited across mitotic or even meiotic
cell divisions (Chinnusamy and Zhu 2009; De Groote et al. 2012). Epigenetic stress
memory may help plants for confront of with subsequent stresses more effectively;
comparative studies on stress-responsive epigenomes and transcriptomes will
enhance our understanding of stress adaptation of plants. As sessile organisms,
plants need to continuously adjust their responses to external stimuli for changing
growth conditions (Zhang et al. 2012). Since the seed dispersal range is often rather
limited, exposure of progeny to the growth conditions of parents is very probable.
The plasticity of plant phenotypes cannot be simply explained by genetic changes
such as point mutations, deletions, insertions, and gross chromosomal rearrangements (Hauser et al. 2011). Since many environmental stresses persist in one or
several plant generations, other adaptation mechanisms must exist. The inheritability of reversible epigenetic modifications, that regulate gene expression without
changing DNA sequence, makes them an attractive alternative mechanism (Boyko
and Kovalchuk 2011). Despite significant advances made in epigenetic research in
recent decades, many questions remain unsolved, especially concerning gene
expression modulation (GEM). Epigenetic marks are enzyme-mediated chemical
modifications of DNA and its associated chromatin proteins. Although they do not
alter the primary sequence of DNA, they also contain inheritable information and
play key roles in regulating genome function. Such modifications including cytosine methylation, posttranslational modifications of histone tails and the histone
core, and the positioning of nucleosomes (histone octamers wrapped with DNA).
These constructs influence the transcriptional state and other functional aspects of
chromatin (Feng and Jacobsen 2011). Adverse environmental phenomena distort
the growth, development, and productivity of crop plants. As a defense, plants have
sophisticated mechanisms to respond and acclimatize to these stresses conditions
by prompt changes at transcriptional and posttranscriptional levels of whole gene
complexes. Various genes belonging to diverse transcription factor families have
been shown to regulate stress-responsive genes, thus playing an important role in
stress signaling. Recently, epigenetic mechanisms have been implicated in the
regulation of the expression of genes related to abiotic or biotic stresses
(Chinnusamy and Zhu 2009). These mechanisms regulate almost all the genetic
15 Plants as Bioreactors for Human Health Nutrients
439