EXO70A2 is critical for the exocyst complex function in Arabidopsis pollen

Vedrana Marković, Fatima Cvrčková, Martin Potocký, Přemysl Pejchar, Eva Kollárová, Ivan Kulich, Lukáš Synek, Viktor Žárský

Posted on: 27 November 2019

Preprint posted on 5 November 2019

Exocyst complex component EXO70A2 plays a vital role in male gametophyte development and is required for successful fertilization

Selected by Chandra Shekhar Misra


Pollen development and tube growth are two important developmental processes in flowering plants, during which the pollen tube carries two sperm cells to the female gametophyte. For successful fertilization, the pollen tube has to navigate within a female tissue to deliver the two sperm cells. This arduous journey is highly regulated and involves maintenance of cell polarity, cell wall secretion and addition of new membrane.

Pollen tubes are a perfect example of polarized tip growth, a process highly controlled by membrane trafficking and polarized secretion. One of the important regulators of polarized secretion is an evolutionarily conserved protein complex called the exocyst, which mediates docking of secretory vesicles at specific sites on the plasma membrane with the help of SNARE proteins. Apart from pollen tube growth, exocyst proteins are also involved in diverse cellular processes requiring targeted secretion such as root hair growth, cytokinesis, trichome and xylem development.

One of the most studied exocyst proteins in plants is EXO70 which arose as a result of duplication and has up to 47 paralogs in rice and 23 in Arabidopsis. Plant-specific EXO70 proteins can be divided into 3 clades: EXO70.1, EXO70.2, and EXO70.3, each of which perform cell or tissue-specific functions, and different isoforms within a clade may also act together in the same cell [1]. The role of several exocyst proteins in pollen germination and tube growth are well understood. For instance, two closely related EXO70C paralogs from the EXO70.2 clade are important for optimal pollen tube tip growth, and several homozygous mutants of the exocyst subunits SEC5a/b, SEC6, Sec8 produce abnormal pollen tube growth resulting in male-specific transmission defects. EXO70A1, a member of clade EXO70.1, is a main sporophytic housekeeping isoform while its paralog EXO70A2 is enriched in pollen, but its function remains largely unknown.

In this study, the authors studied the function of EXO70A2 isoform by mutating the gene and found that the plants defective in EXO70A2 had reduced pollen germination efficiency which impacted pollen-specific transmission of the mutant allele.


Significant findings:

The authors found EXO70A2 to be the closest paralog of EXO70A1, with the two proteins having 72% sequence similarity. EX070A2 was expressed in pollen and based on the known function of its sporophytic tissue-enriched paralog EXO70A1, was predicted to have a role in tip growth.

The authors used CRISPR to create exo70a2 mutant which showed a defect in pollen germination, maturation and tip growth, consistent with the earlier findings from two other exocyst subunit mutants (sec3a and sec8), while no differences were observed in general plant morphology, implicating EXO70A2 to be pollen-specific. Furthermore, the authors found that exo70a2 mutants produced extremely short and wide pollen tubes with highly reduced fertilization capacity, a phenotype they ascribe to the inefficient targeting of secretory vesicles. Authors also found that the abnormal morphology of pollen tube growth could be linked to the mislocalization of cell wall material, an essential ingredient for polarized tip growth in pollen tubes. Similar to the other core exocyst subunits, EXO70A2 showed plasma membrane localization in the growing pollen tube tip, which the authors believe mediates the exocyst interaction with the plasma membrane.

In order to understand if the effect of exo70A2 mutation caused defect in male or female, the authors studied the transmission of the mutant allele using reciprocal crosses between heterozygous exo70a2 and wild-type plants and they found that the pollen-specific transmission efficiency of the mutant allele was heavily compromised. Despite impaired transmission efficiency, the mutation did not cause a complete transmission defect which led the authors to surmise that probably some other isoform of EXO70 might play a role in rescuing the phenotype.

Complementation with GFP:EXO70A2 was able to rescue the phenotype, further confirming the effect of the mutation in EXO70A2 on pollen germination and tube growth. Interestingly, despite the difference on an evolutionary timescale, authors found that EXO70A2 was able to rescue pleiotropic defects caused by a mutation in exo70a1 mutant, suggesting a high degree of functional redundancy between two paralogs EXO70A1 and EXO70A2 in the sporophyte.


What I liked about this preprint and why I think this work is important

Male gametophyte development is an active area of research and although we think we have understood the process well, there are still a lot of missing links to how the whole system works. In that direction, identifying one more important player involved in pollen development is indeed remarkable. I think it is an important contribution to the reproductive biology of plants, also because very little is known regarding the role of membrane trafficking in pollen development.


Questions for the author and future studies

  1.  The authors described how EX070A2 was able to rescue the mutant phenotype of EXO70A1 showing the high degree of functional redundancy between the two paralogs. It would be interesting to see if EXO70A1 is able to rescue the phenotype in exo70a2 during pollen germination and tube growth defect?
  2. EX070A2 has a relatively weak expression in mature pollen compared to other isoforms of EXO70 such as EXO70H3/5. It would be nice to see what would be the effect of these isoforms on pollen development and if the authors anticipate higher pollen development and tube growth defect in case of say double or triple mutants.
  3. The exocyst proteins have an important role in localization of cell wall material and modifying enzymes which impacts the pollen tube growth and is shown by the authors. But do the authors anticipate any effect on the maintenance of pollen tube integrity and rupturing during sperm delivery. This might be important to understand why though we have little effect on pollen tube growth in vivo but the male transmission efficiency is compromised.
  4. Linked to the previous question, it would be important to understand if the effect on pollen tube morphology (width) also remains less affected unlike in vitro grown pollen tubes. For this, though in vivo it would not be possible, but is it possible to check this using Semi in vivo pollen tube growth experiments?
  5. The authors have indicated that the exocyst subunits are typically present in all higher organisms from yeast to mammals and in plants. It would be interesting to explore the phylogenetic conservation of these proteins with regard to their function in other plants such as Physcomitrella patens or in rice.



  1. Viktor Žárský, Juraj Sekereš, Zdeňka Kubátová, Tamara Pečenková, Fatima Cvrčková, Three subfamilies of exocyst EXO70 family subunits in land plants: early divergence and ongoing functional specialization, Journal of Experimental Botany, erz423,

Tags: arabidopsis, double fertilization, exo70a2, exocyst, pollen tube


Read preprint (No Ratings Yet)

Have your say

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up to customise the site to your preferences and to receive alerts

Register here

Also in the developmental biology category:

Notch3 is a genetic modifier of NODAL signalling for patterning asymmetry during mouse heart looping

Tobias Holm Bønnelykke, Marie-Amandine Chabry, Emeline Perthame, et al.

Selected by 06 June 2024

Bhaval Parmar

Developmental Biology

Lipid-Based Transfection of Zebrafish Embryos: A Robust Protocol for Nucleic Acid Delivery

Aslihan Terzi, Tiger Liao, Adrian Jacobo

Selected by 09 May 2024

Roberto Rodríguez-Morales


Topology changes of the regenerating Hydra define actin nematic defects as mechanical organizers of morphogenesis

Yamini Ravichandran, Matthias Vogg, Karsten Kruse, et al.

Selected by 08 May 2024

Rachel Mckeown

Developmental Biology

Also in the plant biology category:

Plasmodesmal closure elicits stress responses

Estee E. Tee, Andrew Breakspear, Diana Papp, et al.

Selected by 12 June 2024

Yueh Cho

Plant Biology

Generalized Biomolecular Modeling and Design with RoseTTAFold All-Atom

Rohith Krishna, Jue Wang, Woody Ahern, et al.

Selected by 24 January 2024

Saanjbati Adhikari


Plant plasmodesmata bridges form through ER-driven incomplete cytokinesis

Ziqiang P. Li, Hortense Moreau, Jules D. Petit, et al.


Plasmodesmata act as unconventional membrane contact sites regulating inter-cellular molecular exchange in plants

Jessica Pérez-Sancho, Marija Smokvarska, Marie Glavier, et al.

Selected by 09 January 2024

Gwendolyn K. Kirschner

Plant Biology

preLists in the developmental biology category:

BSDB/GenSoc Spring Meeting 2024

A list of preprints highlighted at the British Society for Developmental Biology and Genetics Society joint Spring meeting 2024 at Warwick, UK.


List by Joyce Yu, Katherine Brown

GfE/ DSDB meeting 2024

This preList highlights the preprints discussed at the 2024 joint German and Dutch developmental biology societies meeting that took place in March 2024 in Osnabrück, Germany.


List by Joyce Yu

‘In preprints’ from Development 2022-2023

A list of the preprints featured in Development's 'In preprints' articles between 2022-2023


List by Alex Eve, Katherine Brown

preLights peer support – preprints of interest

This is a preprint repository to organise the preprints and preLights covered through the 'preLights peer support' initiative.


List by preLights peer support

The Society for Developmental Biology 82nd Annual Meeting

This preList is made up of the preprints discussed during the Society for Developmental Biology 82nd Annual Meeting that took place in Chicago in July 2023.


List by Joyce Yu, Katherine Brown

CSHL 87th Symposium: Stem Cells

Preprints mentioned by speakers at the #CSHLsymp23


List by Alex Eve

Journal of Cell Science meeting ‘Imaging Cell Dynamics’

This preList highlights the preprints discussed at the JCS meeting 'Imaging Cell Dynamics'. The meeting was held from 14 - 17 May 2023 in Lisbon, Portugal and was organised by Erika Holzbaur, Jennifer Lippincott-Schwartz, Rob Parton and Michael Way.


List by Helen Zenner

9th International Symposium on the Biology of Vertebrate Sex Determination

This preList contains preprints discussed during the 9th International Symposium on the Biology of Vertebrate Sex Determination. This conference was held in Kona, Hawaii from April 17th to 21st 2023.


List by Martin Estermann

Alumni picks – preLights 5th Birthday

This preList contains preprints that were picked and highlighted by preLights Alumni - an initiative that was set up to mark preLights 5th birthday. More entries will follow throughout February and March 2023.


List by Sergio Menchero et al.

CellBio 2022 – An ASCB/EMBO Meeting

This preLists features preprints that were discussed and presented during the CellBio 2022 meeting in Washington, DC in December 2022.


List by Nadja Hümpfer et al.

2nd Conference of the Visegrád Group Society for Developmental Biology

Preprints from the 2nd Conference of the Visegrád Group Society for Developmental Biology (2-5 September, 2021, Szeged, Hungary)


List by Nándor Lipták


The advances in fibroblast biology preList explores the recent discoveries and preprints of the fibroblast world. Get ready to immerse yourself with this list created for fibroblasts aficionados and lovers, and beyond. Here, my goal is to include preprints of fibroblast biology, heterogeneity, fate, extracellular matrix, behavior, topography, single-cell atlases, spatial transcriptomics, and their matrix!


List by Osvaldo Contreras

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.


List by Alex Eve

EMBL Conference: From functional genomics to systems biology

Preprints presented at the virtual EMBL conference "from functional genomics and systems biology", 16-19 November 2020


List by Jesus Victorino

Single Cell Biology 2020

A list of preprints mentioned at the Wellcome Genome Campus Single Cell Biology 2020 meeting.


List by Alex Eve

Society for Developmental Biology 79th Annual Meeting

Preprints at SDB 2020


List by Irepan Salvador-Martinez, Martin Estermann

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020


List by Ana Dorrego-Rivas

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.


List by Ana Dorrego-Rivas

Cell Polarity

Recent research from the field of cell polarity is summarized in this list of preprints. It comprises of studies focusing on various forms of cell polarity ranging from epithelial polarity, planar cell polarity to front-to-rear polarity.


List by Yamini Ravichandran

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20


List by Maiko Kitaoka et al.

3D Gastruloids

A curated list of preprints related to Gastruloids (in vitro models of early development obtained by 3D aggregation of embryonic cells). Updated until July 2021.


List by Paul Gerald L. Sanchez and Stefano Vianello

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)


List by Madhuja Samaddar et al.

EDBC Alicante 2019

Preprints presented at the European Developmental Biology Congress (EDBC) in Alicante, October 23-26 2019.


List by Sergio Menchero et al.

EMBL Seeing is Believing – Imaging the Molecular Processes of Life

Preprints discussed at the 2019 edition of Seeing is Believing, at EMBL Heidelberg from the 9th-12th October 2019


List by Dey Lab

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.


List by Alex Eve

Lung Disease and Regeneration

This preprint list compiles highlights from the field of lung biology.


List by Rob Hynds

Young Embryologist Network Conference 2019

Preprints presented at the Young Embryologist Network 2019 conference, 13 May, The Francis Crick Institute, London


List by Alex Eve

Pattern formation during development

The aim of this preList is to integrate results about the mechanisms that govern patterning during development, from genes implicated in the processes to theoritical models of pattern formation in nature.


List by Alexa Sadier

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019


List by Dey Lab

Zebrafish immunology

A compilation of cutting-edge research that uses the zebrafish as a model system to elucidate novel immunological mechanisms in health and disease.


List by Shikha Nayar