dc.description.abstract | Due to their sessile life style, plants are continuously exposed to a variety of abiotic
and biotic stresses which could potentially hinder their growth, development, productivity
and survival. In this scenario, it appears evident the relevance of epigenetic mechanisms
in assuring growth plasticity to the plant and withstanding stresses through a rapid and
extensive modification of gene expression in a manner that overcomes the restrictions of
a highly stable DNA sequence.
Epigenome landscape is largely related to DNA methylation process, which is
one of the most significant players in the control of plant responses to environmental
changes and stressors. On the other hand, all these responses are also under the control of
an intricate signalling network which strongly involves the phytohormones, whose action
is in turn influenced by epigenetic mechanisms. Despite this information, the complex
mechanisms by which DNA methylation modulates plant stress responses are yet largely
unresolved, mainly with respect to heavy metal stress, for which a metal- and speciesspecific
response was evidenced.
In order to gain further insight into these aspects, in the present work we performed
a comparative transcriptomic analysis on the drm1 drm2 cmt3 (ddc) mutant of A. thaliana,
defective in both maintenance and de novo DNA methylation, and WT plants exposed to
a long lasting (21 days) Cd treatment at 25 and 50 μM concentrations. Attention was
focused on Cd as one of the most toxic pollutants, widespread in both terrestrial and marine
environment. The mutant was chosen as a suitable tool for investigating mechanisms and
molecular processes that act in and are regulated by DNA methylation. Analyses of growth
parameters and targeted cytophysiological features were also carried out.
Concerning the results, transcriptomic analysis highlighted photosynthesis, stress
responses and hormone biosynthesis as the genetic pathways more impacted by Cd
treatment in both ddc mutant and WT. All these pathways are highly relevant for plant
development. A more detailed analysis carried out on the pathways related to the
phytohormones suggested that, under a prolonged heavy metal exposure, plant activity was
directed to enhance and/or maintain the level and signalling of hormones which are
relevant in sustaining the growth (auxins, cytokinins and gibberellins) more than those of
hormones specifically related to stress response (jasmonic acid, abscisic acid and salicylic
acid). This could represent the plant strategy to avoid the negative effects of long-lasting activity of stress-related hormones. Interestingly, such strategy could be more efficient in
ddc mutant than in the WT. Indeed, likely due to a higher genome plasticity conferred to
the mutant by its DNA hypomethylated status, in the ddc mutant the described
transcriptomic differences have already been observed in the treatment with 25 μM Cd,
while in the WT only in the treatment with 50 μM Cd. The outcome of this different
modulation of gene expression was a better growth performance in ddc vs WT, as
evidenced by growth parameters analysis. A tight relationship between the hormonerelated
transcriptomic differences and the different cyto- morphophysiological features of
ddc mutant vs WT under Cd treatment was also revealedUniversità della Calabria, Dipartimento di Biologia, Ecologia e Scienze della Terra. Dottorato di Ricerca in Scienze della Vita. Ciclo XXXI SSD BIO/01 | en_US |