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Doctoral thesis, 2019

Mechanisms of unreduced gamete formation in Arabidopsis thaliana

Yi, Jun;


Polyploidy is a widespread phenomenon in plants, which is commonly believed to arise through the production of unreduced (2n) gametes due to meiotic failure. Despite the importance of unreduced gamete formation for plant polyploidization, the mechanisms leading to their formation are not well understood. Previous work of our group indicated that JASON (JAS) regulates chromosome segregation through affecting the position of organelles, which behave as a physical barrier between the two spindles. In my thesis, I aimed at understanding how JAS affects positioning of the organelles during meiosis in Arabidopsis thaliana. I revealed that during meiosis, JAS was co-localized with markers for the Golgi and the plasma membrane in the organelle band at metaphase II, indicating that a subset of the Golgi apparatus and endomembrane vesicles are components of the organelle band. Maintaining the organelle band relies on the function of the JAS protein. JAS can encode two versions of proteins, a long version including an N-terminal mitochondrial targeting signal (JAS.1) and a short version lacking this sequence (JAS.2). To investigate which version of JAS is functional during meiosis, I tested both versions for their ability to complement the jas mutant. I found that only JAS.2 could complement the jas mutant phenotype. Consistent with the genetic data, localization of JAS.2-GFP under control of a constitutive promoter was the same as JAS-GFP expressed under control of the native promoter that also contained the N-terminal extension, suggesting that most likely JAS.2 is the protein translated in wild type during meiosis. To further characterize the mechanism of JAS function, we performed a suppressor screen with the aim to find mutants that form reduced gametes in the presence of the jas mutation. In this screen, telamon (tel) was isolated as a strong suppressor of jas that can produce many haploid pollen in the jas background. While the organelle band was not restored in jas;tel in meiosis II, meiotic cells were enlarged in the jas;tel mutant. Importantly, tetraploidization of jas suppressed the jas phenotype and led to the production of reduced gametes, supporting the idea that increase of meiocyte size can bypass the requirement of the organelle band. Lastly, I discovered that Eutrema salsugineum that has smaller meiocytes than Arabidopsis thaliana was more sensitive to cold stress and produced increased numbers of diploid pollen. Combined, these results strongly support the idea that meiocyte size impacts on chromosome segregation in meiosis II and suggests that the organelle band is mainly required in species forming small meiocytes. Altogether, this thesis provides novel insights into the mechanism leading to unreduced gamete formation and reveals a new and exciting mechanism that may have facilitated the decrease of pollen size.


Arabidopsis, meiosis, unreduced gametes, polyploid

Published in

Acta Universitatis Agriculturae Sueciae

2019, number: 2019:11
ISBN: 978-91-7760-340-5, eISBN: 978-91-7760-341-2
Publisher: Swedish University of Agricultural Sciences

Authors' information

Yi, Jun
Swedish University of Agricultural Sciences, Department of Plant Biology

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