Date: 12th October 2022
Title: The identification and verification of a gene for Parthenogenesis, the plant embryo development without fertilisation, from apomictic dandelion (Taraxacum), and its use as a tool in breeding line production
Location: Lecture room B5, Forest Sciences Building, Latokartanonkaari 7-9 and remotely via Zoom
Host: Teemu Teeri
Abstract: Parthenogenesis is the spontaneous development of an egg cell into an embryo, so without fertilization and the fusion of gametes. It naturally occurs in a variety of plant species, usually in combination with the omission of meiosis (apomeiosis) and either autogamous (spontaneous) or pseudogamous (through fertilization of the central cell) endosperm production. This together is known as Apomixis (clonal seed production) and as a whole as well as in its separate components has high potential for application in plant breeding: Parthenogenesis in combination with apomeiosis is of particular interest for the maintenance of vigorous F1-hybrids; parthenogenesis alone finds application in doubled haploid (DH) production; and parthenogenesis in alternation with apomeiosis in subsequent generations allows for the connection of germplasm of different ploidy level. Despite these huge interests, the identification of apomixis genes is difficult, mainly as a result of their location in diverged chromosomal regions due to their long asexual history. We have isolated the PARTHENOGENESIS (PAR) gene from apomictic dandelion and shown that it triggers embryo development in unfertilized egg cells also in the related crop species lettuce. The PAR gene was identified via a combined strategy, including genetic and deletion mapping, single cell transcriptomics and CRISPR/Cas knock-out studies. The dominant PAR allele in apomictic dandelion is expressed in egg cells, while the recessive sexual alleles are not. A miniature inverted-repeat transposable element (MITE) was found inserted in the PAR promoter of the dominant allele, promoting PAR expression. Interestingly, a similar MITE was found in the promoter of the PAR gene in apomictic hawkweed, indicating parallel evolution of parthenogenesis in different species. Recessive par alleles are expressed in the pollen of sexual dandelion. We hypothesize that the PAR gene product silences inhibitors of embryogenesis in the egg cell, through fertilization in the sexuals and direct production in the apomicts, initiating embryo development.
Dr. Kitty Vijverberg graduated with her BSc in Biochemistry and MSc in Biology from the University of Amsterdam, the Netherlands, and with her PhD in Molecular Plant Taxonomy from the same university. Since her PhD she has been a researcher in Plant Reproduction and Flower Development at different institutes on the same or related projects. Her main contribution is in the characterization and identification of apomixis genes in dandelion. She performed genetic (fine) mapping of the gene for apomeiosis in dandelion, DIPLOSPOROUS, and was involved in the physical mapping and chromosome walking to further define the DIP locus. In 2005-2006 Kitty stayed at Ueli Grossniklaus’ lab of Plant Developmental Genetics at the University of Zurich in Switzerland. Here, she was one of the first to use Laser Assisted Microdissection to isolate single cell populations in plants and developed a method to determine the transcriptomes of cells of the female gametophyte. This method formed the basis of her comparative egg cell transcriptome study in dandelions to identify a gene for PARTHENOGENESIS as well as obtaining a major grant to do this analysis, of which the results are presented today.
In addition to the apomixis projects, Kitty was involved for several years in research on flower development in Petunia with a focus on the role of miRNAs therein. From this research she knows Prof. Teemu Teeri and Paula Elomaa and their work in Gerbera, a species of the Asteraceae family as is dandelion, and therefore always of special attention to her. One project Kitty is currently involved in is a genomic and floral transcriptomic study in dandelions with the aim of determining the genetic basis underlying the floral developmental aspects that are unique to Asteraceae. She recently published a paper on the homology of the pappus in dandelion with the petals, that are usually located in the outer floral whorl.