| dc.description.abstracteng | Alpine habitats are shaped by harsh abiotic conditions and cold climates. Plant life in
such habitats is challenging, as environmental influence can alter the conditions for
development and reproduction.
More specifically, phenotypic plasticity of morphological traits can be influenced by
temperature stress. Temperature stress can also affect epigenetic and gene expression
profiles, which may have an impact on acclimation and adaptation of the species.
Polyploidy seems to affect the DNA methylation profiles, while distribution patterns
suggest that it could be advantageous under cold conditions.
Nevertheless, little is known about non -model plants, whether temperature stress can
induce methylation changes depending on the cytotypes of the individuals, to what
extent a treatment shift can induce epigenetic responses and how they are depicted in
phenotypic plasticity and reproduction of the species. Furthermore, it remains vague
how cold stress is translated in gene expression changes under different cytotypes and
how such a putative response is framed through gene set pathways and epigenetic
control.
The perennial alpine plant Ranunculus kuepferi was utilized to investigate the
correlations of cold stress with polyploidy, mode of reproduction, phenotypic plasticity,
epigenetics, gene expression and geographical parthenogenesis . The species is mainly
found in the wild with diploid and autotetraploid cytotypes, which are mostly sexual
and facultative apomicts, respectively.
Diploid and autotetraploid individuals were placed in two climate chambers and
exposed to cold (+7°C day/+2°C night, -1°C cold shocks for three nights per week) and
warm (control) (+15°C day/+10°C night) temperature treatments in climate growth
chambers for four consecutive flowering periods and shifted from one condition to the
other after the first flowering period.
Methylation-sensitive amplified fragment- length polymorphism markers were applied
for the first two years, to screen possible genome-wide methylation alterations triggered
by temprerature treatments and treatment shifts. For the second year of t emperature
treatments, morphological traits (height, leaves and flowers) and the proportion of well-
developed seeds were measured as fitness indicators, while flow cytometric seed
screening (FCSS) was utilized to determine the reproduction mode. Subsequently,
comparisons with patterns of methylation-sensitive amplified fragment- length
polymorphisms (MS-AFLPs/MSAPs) regarding the same year of treatment were
conducted. Finally, for the last year of treatment, both cytotypes were investigated for
their gene expression profiles via transcriptome sequencing and qRT-PCR. The datasets
were analyzed for four predefined groups with respect to treatment (Cold/Warm) and
ploidy level (Diploid/Tetraploid).
DNA methylation profiles showed temperature sensitivity and propose a ploidy effect
for both years of analysis. Likewise, the treatment shift had an impact on both cytotypes,
resulting in significantly less epiloci, regardless of the shift’s direction. Such correlations
of ploidy level and epigenetic profiles may reflec t DNA methylation dynamics during
cold acclimation. The AMOVA results are in line with the hypothesis of cold stress
influencing the epigenetic patterns, while they also depict the DNA methylation
dynamics of tetraploids, as a response to temperature treatment shift.
Concerning the phenotypic plasticity of the species under temperature treatments, the
potential of acclimation under environmental conditions is underlined, as diploids grow
better under warm conditions and tetraploids perform better in cold treatments, while
the expressed morphological traits are linked with epigenetic patterns. Moreover, cold
stress reduced the reproduction fitness but did not induce apomixis in diploid
individuals. These results confirm the different niche preferences of cytotypes in natural
populations and empower the geographical parthenogenesis scenario, which is
previously proposed for the species.
Cold acclimation of the cytotypes is further indicated by gene expression profiles.
Overall, diploid individuals altered more gene set pathways than tetraploid ones, and
suppressed pathways involved in ion/cation homeostasis. Gene Set Pathways mostly
activated under tetraploids are related to cell wall and plasma membrane. Thus,
tetraploids seem to be better acclimated to cold conditions, enabling them to colonize
colder climatic areas in the Alps. Finally, an epigenetic background for gene regulation
in response to temperature conditions is indicated. | de |