@phdthesis{Blacha2009,
  author    = {Blacha, Anna Maria},
  title     = {Investigating the role of regulatory genes in heterosis for superior growth and biomass production in Arabidopsis thaliana},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-46146},
  school      = {Universit{\"a}t Potsdam},
  year      = {2009},
  abstract  = {'Heterosis' is a term used in genetics and breeding referring to hybrid vigour or the superiority of hybrids over their parents in terms of traits such as size, growth rate, biomass, fertility, yield, nutrient content, disease resistance or tolerance to abiotic and abiotic stress. Parental plants which are two different inbred (pure) lines that have desired traits are crossed to obtain hybrids. Maximum heterosis is observed in the first generation (F1) of crosses. Heterosis has been utilised in plant and animal breeding programs for at least 90 years: by the end of the 21st century, 65\% of worldwide maize production was hybrid-based. Generally, it is believed that an understanding of the molecular basis of heterosis will allow the creation of new superior genotypes which could either be used directly as F1 hybrids or form the basis for the future breeding selection programmes. Two selected accessions of a research model plant Arabidopsis thaliana (thale cress) were crossed to obtain hybrids. These typically exhibited a 60-80\% increase of biomass when compared to the average weight of both parents. This PhD project focused on investigating the role of selected regulatory genes given their potentially key involvement in heterosis. In the first part of the project, the most appropriate developmental stage for this heterosis study was determined by metabolite level measurements and growth observations in parents and hybrids. At the selected stage, around 60 candidate regulatory genes (i.e. differentially expressed in hybrids when compared to parents) were identified. Of these, the majority were transcription factors, genes that coordinate the expression of other genes. Subsequent expression analyses of the candidate genes in biomass-heterotic hybrids of other Arabidopsis accessions revealed a differential expression in a gene subset, highlighting their relevance for heterosis. Moreover, a fraction of the candidate regulatory genes were found within DNA regions closely linked to the genes that underlie the biomass or growth heterosis. Additional analyses to validate the role of selected candidate regulatory genes in heterosis appeared insufficient to establish their role in heterosis. This uncovered a need for using novel approaches as discussed in the thesis. Taken together, the work provided an insight into studies on the molecular mechanisms underlying heterosis. Although studies on heterosis date back to more than one hundred years, this project as many others revealed that more investigations will be needed to uncover this phenomenon.},
  language  = {en}
}
@phdthesis{Andorf2011,
  author    = {Andorf, Sandra},
  title     = {A systems biological approach towards the molecular basis of heterosis in Arabidopsis thaliana},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51173},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Heterosis is defined as the superiority in performance of heterozygous genotypes compared to their corresponding genetically different homozygous parents. This phenomenon is already known since the beginning of the last century and it has been widely used in plant breeding, but the underlying genetic and molecular mechanisms are not well understood. In this work, a systems biological approach based on molecular network structures is proposed to contribute to the understanding of heterosis. Hybrids are likely to contain additional regulatory possibilities compared to their homozygous parents and, therefore, they may be able to correctly respond to a higher number of environmental challenges, which leads to a higher adaptability and, thus, the heterosis phenomenon. In the network hypothesis for heterosis, presented in this work, more regulatory interactions are expected in the molecular networks of the hybrids compared to the homozygous parents. Partial correlations were used to assess this difference in the global interaction structure of regulatory networks between the hybrids and the homozygous genotypes. This network hypothesis for heterosis was tested on metabolite profiles as well as gene expression data of the two parental Arabidopsis thaliana accessions C24 and Col-0 and their reciprocal crosses. These plants are known to show a heterosis effect in their biomass phenotype. The hypothesis was confirmed for mid-parent and best-parent heterosis for either hybrid of our experimental metabolite as well as gene expression data. It was shown that this result is influenced by the used cutoffs during the analyses. Too strict filtering resulted in sets of metabolites and genes for which the network hypothesis for heterosis does not hold true for either hybrid regarding mid-parent as well as best-parent heterosis. In an over-representation analysis, the genes that show the largest heterosis effects according to our network hypothesis were compared to genes of heterotic quantitative trait loci (QTL) regions. Separately for either hybrid regarding mid-parent as well as best-parent heterosis, a significantly larger overlap between the resulting gene lists of the two different approaches towards biomass heterosis was detected than expected by chance. This suggests that each heterotic QTL region contains many genes influencing biomass heterosis in the early development of Arabidopsis thaliana. Furthermore, this integrative analysis led to a confinement and an increased confidence in the group of candidate genes for biomass heterosis in Arabidopsis thaliana identified by both approaches.},
  language  = {en}
}