| dc.description.abstracteng | Neutral lipids, such as triacylglycerol (TAG) and wax are essential metabolites for plants. TAG is the
most abundant storage compound in all eukaryotes. It plays an important role in plant germination
but also in lipid homeostasis upon stress. Wax is a mixture of aliphatic compounds, which all together
form a hydrophobic film, covering all aerial parts of plants. This lipid-based barrier protects plants
from environmental threats and an uncontrolled loss of water. The biosynthesis of those two lipid
classes is well studied, however little is known about its regulation upon stress. Hence, this thesis
focused on revealing the function of wax and TAG biosynthesis upon wounding in Arabidopsis
thaliana.
Wounding mimics herbivore attack or mechanical tissue disruption and is one of the most common
plant stresses. The main wound-signal is the hormone jasmonoyl-isoleucine (JA-Ile), whereas wax and
TAG biosynthesis was described to be regulated by on another hormone - abscisic acid (ABA). It is
shown in this study that genes coding for enzymes of the surface wax synthesis as well as those of the
last steps of the TAG biosynthesis are induced upon wounding, mainly in a JA-Ile-independent but
ABA dependent manner. However, on the metabolite level, wax accumulation after wounding is
diminished in JA-Ile-deficient plants and decreased in ABA-reduced plants. However, the enrichment
in TAG is independent of JA-Ile and ABA signaling. To dissect the wound from the drought stress
response, wounding experiments in high humidity were conducted. It was shown, that high humidity
prevents the wound-induced wax accumulation in Arabidopsis leaves and moreover, that the ABAdependent transcription factor MYB96 is a key regulator of wax biosynthesis upon wounding. The
data presented in this study led to the conclusion that wax is accumulating upon wounding to seal the
wounding site, whereas TAG accumulation serves as storage for the acyl-moieties of the plastidial
membrane lipids.
In addition it is shown, that MYB41, another ABA-dependent MYB transcription factor of the R2-R3
family-acts as a negative regulator of wax biosynthesis in Arabidopsis inflorescence stems. MYB41
suppresses the expression of the main fatty acid reductase in inflorescence stems, CER4/FAR3, and
therefore reduces the amount of primary alcohols in the surface wax. A collection of myb41 mutants
helped to characterize regions in the MYB41 protein, which are important for its activity. | de |