Function of Cuticular Waxes in Plant Response to Wounding
by Milena Lewandowska
Date of Examination:2019-06-24
Date of issue:2019-08-27
Advisor:Prof. Dr. Ivo Feußner
Referee:Prof. Dr. Andrea Polle
Referee:Prof. Dr. Ljerka Kunst
Persistent Address:
http://dx.doi.org/10.53846/goediss-7625
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Abstract
English
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.
Keywords: wounding response; cuticular wax; triacylglycerol biosynthesis; regulation of wax biosynthesis
