Genetic information is fundamental in biology. It is stored in all genomes,
crucial to generating and maintaining a new organism. The biological importance of
DNA lies in its role as a carrier of genetic information and how it is expressed under
specific conditions. Among the different ways of controlling the manifestation of
genomic information (or gene expression), epigenetic mechanisms have been
highlighted. These mechanisms are diverse, multifunctional, and profoundly affect the
plant's molecular physiology. Cytosine methylation and demethylation - one of the
best-studied epigenetic mechanisms - is a dynamic process that influences,
respectively, the down- and up-regulation of target genes. The referred chemical
modifications occur in response to developmental processes and environmental
variations, and have their biological value accentuated as they can be passed on to
subsequent generations. This inheritance mechanism conducts ‘states of gene
expression’ to new cells and even to the offspring, allowing them to be ‘more adequate’
to the changing environment. The possibility of inheriting such chemical modifications
defies our understanding of the hereditary process, opening new perceptions and
practical implications. This chapter aims to address the cytosine methylation and
demethylation effects in plants. In the present review, we deal with how cytosine
(de)methylation occurs in plant genomes, their participation in the biotic and abiotic
stress responses, the recent studies for its use in crop breeding, and the epigenetic
inheritance issue, which is a matter of intense debate.
Keywords: Abiotic stress, Biotic stress, De novo methylation, DNA methyltransferase, DNA demethylase, Epigenetic inheritance, Gene expression, Methylation maintenance, Non-coding RNA, Plant epigenetics, Plant breeding, RdDM pathway, RISC complex.
