The role of pollen for the transfer of apomixis into sexual populations of the genus Boechera (Brassicaceae)
Date
2020-01-13
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-0630-7954
Type
Thesis
Degree Level
Masters
Abstract
Besides sexual reproduction, certain flowering plants reproduce clonally by the asexual propagation of seeds (apomixis). Engineering the apomixis trait in major crop plants, which predominantly reproduce sexually, would greatly simplify complex breeding schemes, and would enable the fixation and maintenance of valuable accessions and their associated traits. Hence, understanding the transfer and dispersion of apomixis in natural populations is of great interest to breeders and evolutionary biologists, although our understanding of this process is clouded by ploidy barriers and self-incompatibilities. Based on the analysis of pollen and flow cytometric seed screens in the pseudogamous, diploid apomixis model plant Boechera (Brassicaceae), some 'unbalanced' apomicts may produce meiotically-reduced, fertile pollen, enabling recurrent crossing into purely sexual accessions to explore the mechanism underlying the phylogenetic dispersion of the apomictic phenotype. Hence, we analyzed Boechera pollen to establish pollen classes based on their germination rate, fitness and ploidy. We identified one sexual and two apomictic pollen classes. Then, we tested the following hypotheses: (i) unreduced apomictic pollen is favored over reduced apomictic pollen during central cell fertilization in apomictic embryo sacs, and (ii) only meiotically-reduced apomictic pollen enables the spread of apomixis into sexual populations. Therefore we performed 4727 inter- and intraspecific crosses within and across five Boechera species. The frequencies of apomixis transfer and segregation patterns were evaluated by flow cytometric seed screens and by the presence/absence of two hypothesized apomeiosis factors (i.e. APOLLO apomictic allele, UPGRADE2) in parental plants and their F1 progenies. To test for inheritance of the apomictic phenotype we analyzed the seed set and presence of the apomixis factors in F2 progeny. In summary, homoploid hybridization can lead to the establishment of highly facultative or even obligate apomicts within a single generation. This continuing comprehensive backcrossing strategy will narrow our search for contributing genomic regions, and identify additional factors underlying apomictic reproduction in Boechera.
Description
Keywords
Apomixis, Breading, Boechera, Hybridization, Pollen
Citation
Degree
Master of Science (M.Sc.)
Department
Plant Sciences
Program
Agriculture and Bioresource Engineering