Home About Browse Search
Svenska


Mechanisms of unreduced gamete formation in Arabidopsis thaliana

Yi, Jun (2019). Mechanisms of unreduced gamete formation in Arabidopsis thaliana. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2019:11
ISBN 978-91-7760-340-5
eISBN 978-91-7760-341-2
[Doctoral thesis]

[img] PDF - Published Version
681kB

Abstract

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.

Authors/Creators:Yi, Jun
Title:Mechanisms of unreduced gamete formation in Arabidopsis thaliana
Alternative abstract:
LanguageAbstract
Swedish

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.

Polyploiditet är ett utbrett fenomen bland växter, som tros uppstå genom produktion av oreducerade (2n-) gameter vid misslyckad meios. Trots betydelsen av oreducerade gameter för polyploiditet, är kunskapen om de grundläggande mekanismerna fortfarande bristfälliga. Tidigare forskning i vår grupp indikerar att JASON (JAS), reglerar uppdelning av kromosomer genom att påverka organellernas position, vilka utgör en fysisk barriär mellan kärnspolarna.

Målet med min avhandling är att förstå hur JAS påverkar organellernas position under meiosen hos Arabidopsis thaliana. Jag fann att under meiosen var JAS sammankopplad med markörer för Golgi-apparaten och plasma membranet i ett organellaggregat under metafas II, vilket indikerar att en del av dess vesiklar utgör komponenter i organellaggregatet. Upprätthållandet av detta organellaggregat är beroende av JAS-proteinets funktion.

JAS kan koda för två typer av proteiner, en lång version som inkluderar en N-terminal sekvens med en signal för transport till mitokondrien (JAS.1) och en kort version utan denna sekvens (JAS.2). För att undersöka vilken version som är aktiv vid meios, testade jag bådas förmåga att komplementera jas-mutanten. Jag fann att endast JAS.2 kunde komplementera jas-mutantens fenotyp. I överensstämmelse med genetiska data, visade lokalisering av JAS.2-GFP under kontroll av en konstitutiv promotor samma uttryck som JAS-GFP under kontroll av dess naturliga promotor som också innehåller N-terminalsekvensen, vilket tyder på att det troligtvis är JAS.2-proteinet som translateras vid meiosen.

För att vidare karaktärisera mekanismen för JAS funktion utförde vi en suppressor-screen med målet att hitta mutanter som bildar reducerade gameter i närvaro av jas-mutationen. I denna screen identifierades telamon (tel) som en stark undertryckare av jas som kan producera många haploida pollen i jas-bakrund. De meiotiska cellerna var förstorade i jas:tel-mutanten, men organellaggregatet var inte återställt. Tetraploidisering av jas undertryckte dess fenotyp och ledde till produktion av reducerade gameter, vilket stödjer idén att en ökning av storleken på meiotiska celler kan kringgå behovet av ett organellaggregat. Slutligen upptäckte jag att Eutrema salsugineum som har mindre meiotiska celler än Arabidopsis thaliana, är mer känslig för köldstress och producerar ett ökat antal diploida pollen. Dessa resultat stödjer idén att storleken på de meiotiska cellerna påverkar separationen av kromosomer i meios II och tyder på att organellaggregatet huvudsakligen behövs i arter med små meiotiska celler.

Sammanfattningsvis ger denna avhandling ny insikt om oreducerad gametbildning och uppenbarar en ny och spännande mekanism som kan ha främjat minskad pollenstorlek.

Series/Journal:Acta Universitatis Agriculturae Sueciae (1652-6880)
Year of publishing :2019
Depositing date:22 August 2109
Number:2019:11
Number of Pages:53
Papers/manuscripts:
NumberReferences
IBrownfield L.*¤, Yi J.¤, Jiang H., Minina E.A., Twell D., Köhler C. (2015). Organelles maintain spindle position in plant meiosis. Nat Commun. doi: 10.1038/ncomms7492. * Corresponding author. ¤ Equal contribution
IICabout S., Leask M.P., Varghese S., Yi J., Peters B., Liu C.L., Köhler C., Brownfield L. (2017) The Meiotic Regulator JASON Utilizes Alternative Translation Initiation Sites to Produce Differentially Localized Forms. J. Exp. Bot. 68:4205-4217.
IIIYi J., Kradolfer D., Köhler C.*. Meiocyte size is a determining factor for unreduced gamete formation in Arabidopsis thaliana. (submitted/manuscript)
Place of Publication:Uppsala
Publisher:Department of Plant Biology, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-7760-340-5
ISBN for electronic version:978-91-7760-341-2
ISSN:1652-6880
Language:English
Publication Type:Doctoral thesis
Article category:Other scientific
Full Text Status:Public
Agris subject categories.:F Plant production > F30 Plant genetics and breeding
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Genetics (medical genetics to be 30107 and agricultural genetics to be 40402)
Agrovoc terms:Arabidopsis thaliana, meiosis, gametes, polyploidy
Keywords:Arabidopsis, meiosis, unreduced gametes, polyploid
URN:NBN:urn:nbn:se:slu:epsilon-p-100970
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-100970
ID Code:16286
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Department of Plant Biology (from 140101)
Deposited By: SLUpub Connector
Deposited On:22 Aug 2019 11:00
Metadata Last Modified:22 Aug 2019 11:00

Repository Staff Only: item control page

Downloads

Downloads per year (since September 2012)

View more statistics

Downloads
Hits