Molecular mechanisms underlying thermal sensitivity of male reproduction
Lead Research Organisation:
John Innes Centre
Department Name: Cell and Develop Biology
Abstract
Like humans, most flowering plants reproduce sexually. Sexual reproduction in flowering plants is important, as it produces the seeds that comprise 60% of our food.
Sexual reproduction, especially on the male side, is the stage of plant life most vulnerable to temperature damage. For example, heat stress causes a dramatic decrease in the yield of major crops such as wheat and rice, primarily due to impaired male (pollen) development. As temperature extremes caused by climate change become more frequent, understanding temperature's impact on plant fertility is crucial for feeding the world.
Recently, we discovered that defects in a male tissue called tapetum are the likely cause of thermal sensitivity during male development. Tapetum provides nutrition to the developing pollen, and under high temperature the tapetum becomes abnormally vacuolated and the pollen grains are unable to mature. We also developed state-of-the-art methods for tapetal cell isolation and gene expression studies, and found that a gene regulatory mechanism called DNA methylation is important for tapetal thermotolerance. Employing a genetic screen, we identified two mutant plants with enhanced fertility at high temperature.
Our findings and technical advances put us in a unique position to understand the molecular mechanisms underlying male thermosensitivity. Our specific objectives are to: 1) reveal the molecular basis of tapetal sensitivity to heat, 2) understand how the DNA methylation pathway mediates heat tolerance in the tapetum, and 3) uncover novel genes involved in reproductive thermotolerance. We believe knowledge generated from this work will lay a solid foundation for understanding heat sensitivity during male reproduction, and can be exploited to improve the resilience of crops to heat stress, or engineer conditional male sterility lines valuable for hybrid breeding.
Sexual reproduction, especially on the male side, is the stage of plant life most vulnerable to temperature damage. For example, heat stress causes a dramatic decrease in the yield of major crops such as wheat and rice, primarily due to impaired male (pollen) development. As temperature extremes caused by climate change become more frequent, understanding temperature's impact on plant fertility is crucial for feeding the world.
Recently, we discovered that defects in a male tissue called tapetum are the likely cause of thermal sensitivity during male development. Tapetum provides nutrition to the developing pollen, and under high temperature the tapetum becomes abnormally vacuolated and the pollen grains are unable to mature. We also developed state-of-the-art methods for tapetal cell isolation and gene expression studies, and found that a gene regulatory mechanism called DNA methylation is important for tapetal thermotolerance. Employing a genetic screen, we identified two mutant plants with enhanced fertility at high temperature.
Our findings and technical advances put us in a unique position to understand the molecular mechanisms underlying male thermosensitivity. Our specific objectives are to: 1) reveal the molecular basis of tapetal sensitivity to heat, 2) understand how the DNA methylation pathway mediates heat tolerance in the tapetum, and 3) uncover novel genes involved in reproductive thermotolerance. We believe knowledge generated from this work will lay a solid foundation for understanding heat sensitivity during male reproduction, and can be exploited to improve the resilience of crops to heat stress, or engineer conditional male sterility lines valuable for hybrid breeding.
Technical Summary
Male reproductive development is the most sensitive stage to heat stress during the life cycle of flowering plants. Understanding the molecular basis of thermosensitivity during male reproductive development is exceedingly important to sustain crop yield as extreme temperatures are forecast due to climate change.
Although the temperature sensitivity of male reproduction has been recognised as an important issue for many years, its molecular basis is unclear. Recently, we have: 1) developed Arabidopsis thaliana as a model for understanding this issue, and identified a heat treatment that is easily realised in our growth chambers and captures substantial and reproducible male sensitivity to heat; 2) discovered that a specific cell type in the male organ, called the tapetum (or tapetal cells), likely underlies the thermosensitivity during male development; 3) established the first protocol for pure tapetal cell isolation via fluorescence-activated cell sorting, and state-of-the-art methods for single-cell-type RNA and DNA methylome sequencing; 4) found that the RNA-directed DNA methylation pathway (RdDM) specifically methylates genes in the tapetum and mediates the tolerance of tapetum to heat; and 5) isolated mutants with enhanced heat resistance during male reproduction.
These findings and technical advances put us in a unique position to carry out this proposed work, which will elucidate the mechanisms of male heat sensitivity. Our specific objectives are to: 1) reveal the molecular basis of tapetal sensitivity to heat, 2) understand how RdDM mediates heat tolerance in the tapetum, and 3) uncover novel genes involved in reproductive thermotolerance. Through these objectives, we will discover the genetic and epigenetic mechanisms of male thermosensitivity, which can be exploited to improve the resilience of crops to temperature stress.
Although the temperature sensitivity of male reproduction has been recognised as an important issue for many years, its molecular basis is unclear. Recently, we have: 1) developed Arabidopsis thaliana as a model for understanding this issue, and identified a heat treatment that is easily realised in our growth chambers and captures substantial and reproducible male sensitivity to heat; 2) discovered that a specific cell type in the male organ, called the tapetum (or tapetal cells), likely underlies the thermosensitivity during male development; 3) established the first protocol for pure tapetal cell isolation via fluorescence-activated cell sorting, and state-of-the-art methods for single-cell-type RNA and DNA methylome sequencing; 4) found that the RNA-directed DNA methylation pathway (RdDM) specifically methylates genes in the tapetum and mediates the tolerance of tapetum to heat; and 5) isolated mutants with enhanced heat resistance during male reproduction.
These findings and technical advances put us in a unique position to carry out this proposed work, which will elucidate the mechanisms of male heat sensitivity. Our specific objectives are to: 1) reveal the molecular basis of tapetal sensitivity to heat, 2) understand how RdDM mediates heat tolerance in the tapetum, and 3) uncover novel genes involved in reproductive thermotolerance. Through these objectives, we will discover the genetic and epigenetic mechanisms of male thermosensitivity, which can be exploited to improve the resilience of crops to temperature stress.
Planned Impact
The impact of temperature stress on crop yield is enormous. For example, heat stress during the flowering of rapeseed brassica causes a decrease in seed yield by 52%. For rice, each 1C increase in growing-season night-time temperature leads to a grain yield loss by 10%. As temperature extremes caused by climate change become more frequent, understanding temperature's impact on crop fertility is therefore crucial for feeding the world.
The proposed project aims to reveal the mechanisms underlying heat sensitivity of male reproductive development. The knowledge gained from this research will be of significant benefit to plant breeders and biotech companies as it directly relates to crop yield and therefore to the UK public in general on an economic and social scale, providing food security for the future.
Collaboration between fundamental research, plant breeding, and biotechnology plays a major role in agricultural improvement. We aim to identify the genes and processes that are required for thermotolerance during male reproduction through the proposed research. Given the conservation of reproductive genetics across plant species, knowledge gained from this work in Arabidopsis thaliana can be exploited to generate heat-tolerant lines of Brassica and rice, or heat-sensitive (i.e. conditional) male sterile lines important for hybrid breeding. Our current explorative work on Brassica and collaboration on rice, will allow the translation of gained knowledge to agronomy improvement. Besides explicit findings of new genes that are involved in the heat sensitivity of reproductive development, this proposed research will also generate a wealth of DNA methylomic and transcriptomic data on an important cell type (the tapetal cell) in two temperatures (21C and 29C). These data are not only invaluable for scientists, but may also be used by breeders and agrobiotech industry as markers for breeding or research, which in the long term will impact positively on agricultural productivity and the UK's economy.
I will engage with the public via the Norfolk Teacher Scientist Network (TSN) to teach school children, focusing on the specifics of our work in relation to the national curriculum, including topics such as specialised plant cells and their function in development. I will make use of the External Relations Director and the Communications team at JIC to issue press releases, in an accessible format, to publicise the potential of epigenetics in crop enhancement and the outcomes of this Grant. Through meeting with scientists from breeding and agro-biotech companies and intellectual property (IP) experts, we will identify potential applications and IP targets, thus applying this research quickly and directly to crop yield improvement. The proposed project therefore has strong economic impacts that will add to the UK's economic competitiveness in addition to the social implications of maintaining a sustainable level of food production in the future.
The proposed project aims to reveal the mechanisms underlying heat sensitivity of male reproductive development. The knowledge gained from this research will be of significant benefit to plant breeders and biotech companies as it directly relates to crop yield and therefore to the UK public in general on an economic and social scale, providing food security for the future.
Collaboration between fundamental research, plant breeding, and biotechnology plays a major role in agricultural improvement. We aim to identify the genes and processes that are required for thermotolerance during male reproduction through the proposed research. Given the conservation of reproductive genetics across plant species, knowledge gained from this work in Arabidopsis thaliana can be exploited to generate heat-tolerant lines of Brassica and rice, or heat-sensitive (i.e. conditional) male sterile lines important for hybrid breeding. Our current explorative work on Brassica and collaboration on rice, will allow the translation of gained knowledge to agronomy improvement. Besides explicit findings of new genes that are involved in the heat sensitivity of reproductive development, this proposed research will also generate a wealth of DNA methylomic and transcriptomic data on an important cell type (the tapetal cell) in two temperatures (21C and 29C). These data are not only invaluable for scientists, but may also be used by breeders and agrobiotech industry as markers for breeding or research, which in the long term will impact positively on agricultural productivity and the UK's economy.
I will engage with the public via the Norfolk Teacher Scientist Network (TSN) to teach school children, focusing on the specifics of our work in relation to the national curriculum, including topics such as specialised plant cells and their function in development. I will make use of the External Relations Director and the Communications team at JIC to issue press releases, in an accessible format, to publicise the potential of epigenetics in crop enhancement and the outcomes of this Grant. Through meeting with scientists from breeding and agro-biotech companies and intellectual property (IP) experts, we will identify potential applications and IP targets, thus applying this research quickly and directly to crop yield improvement. The proposed project therefore has strong economic impacts that will add to the UK's economic competitiveness in addition to the social implications of maintaining a sustainable level of food production in the future.
People |
ORCID iD |
Xiaoqi Feng (Principal Investigator) |
Publications
Lawrence E
(2019)
Natural Variation in TBP-ASSOCIATED FACTOR 4b Controls Meiotic Crossover and Germline Transcription in Arabidopsis
in Current Biology
Zhao L
(2023)
Dynamic chromatin regulatory programs during embryogenesis of hexaploid wheat.
in Genome biology
Ding P
(2021)
Chromatin accessibility landscapes activated by cell-surface and intracellular immune receptors.
in Journal of experimental botany
He S
(2022)
DNA methylation dynamics during germline development.
in Journal of integrative plant biology
Buttress T
(2022)
Histone H2B.8 compacts flowering plant sperm through chromatin phase separation
in Nature
Christophorou N
(2020)
AXR1 affects DNA methylation independently of its role in regulating meiotic crossover localization.
in PLoS genetics
Bloomer RH
(2020)
The Arabidopsis epigenetic regulator ICU11 as an accessory protein of Polycomb Repressive Complex 2.
in Proceedings of the National Academy of Sciences of the United States of America
Long J
(2021)
Nurse cell--derived small RNAs define paternal epigenetic inheritance in Arabidopsis.
in Science (New York, N.Y.)
Manavella P
(2023)
Beyond transcription: compelling open questions in plant RNA biology
in The Plant Cell
Description | 1. We have confirmed our hypothesis that RdDM in the tapetum is sensitive to heat and mediates male sensitivity. 2. We have performed RNA-seq and Methyl-seq using isolated tapetal cells from wild type and the RdDM mutant plants, each genotype grown at two temperatures, high temperature (29C) and normal temperature (21C). Through this, we have identified regions in the tapetal genome that are differentially methylated at high temperature and/or in the RdDM mutant. We found high temperature causes thousands of loci to gain and lose significant amount of DNA methylation, respectively. By correlating with the transcriptomic data, we have identified putative genes responsible for RdDM-mediated heat tolerance in the tapetum. Ectopic expression and CRISPR knockout of these candidate genes have been performed to test their roles in heat response. 3. We have completed in-depth phenotypic characterization and two backcrosses for the two heat-resistant mutants we isolated. We have sequenced the two mutants with enhanced male fertility at high temperature via Illumina sequencing. |
Exploitation Route | The knowledge obtained from this study will lay a solid foundation for understanding heat sensitivity of male reproduction, knowledge that will contribute to improving the resilience of crops to temperature stress. |
Sectors | Agriculture Food and Drink Environment |
Description | EMBO Young Investigator |
Amount | € 15,000 (EUR) |
Organisation | European Molecular Biology Organisation |
Sector | Charity/Non Profit |
Country | Germany |
Start | 01/2019 |
End | 12/2022 |
Description | Marie Sklodowska-Curie Actions Fellowship |
Amount | £173,026 (GBP) |
Organisation | Marie Sklodowska-Curie Actions |
Sector | Charity/Non Profit |
Country | Global |
Start | 03/2021 |
End | 03/2023 |
Description | Christine Mezard |
Organisation | French National Institute of Agricultural Research |
Department | INRA Versailles |
Country | France |
Sector | Academic/University |
PI Contribution | We are evaluating the effect of AXR1 on the DNA methylation in male meiocytes |
Collaborator Contribution | They identified the AXR1 gene, whose mutation affects recombination during meiosis and generally the DNA methylome in somatic tissues. |
Impact | This has led to a publication in Plos Genetics in 2020. Meiotic crossovers (COs) are important for reshuffling genetic information between homologous chromosomes and they are essential for their correct segregation. COs are unevenly distributed along chromosomes and the underlying mechanisms controlling CO localization are not well understood. We previously showed that meiotic COs are mis-localized in the absence of AXR1, an enzyme involved in the neddylation/rubylation protein modification pathway in Arabidopsis thaliana. Here, we report that in axr1-/-, male meiocytes show a strong defect in chromosome pairing whereas the formation of the telomere bouquet is not affected. COs are also redistributed towards subtelomeric chromosomal ends where they frequently form clusters, in contrast to large central regions depleted in recombination. The CO suppressed regions correlate with DNA hypermethylation of transposable elements (TEs) in the CHH context in axr1-/- meiocytes. Through examining somatic methylomes, we found axr1-/- affects DNA methylation in a plant, causing hypermethylation in all sequence contexts (CG, CHG and CHH) in TEs. Impairment of the main pathways involved in DNA methylation is epistatic over axr1-/- for DNA methylation in somatic cells but does not restore regular chromosome segregation during meiosis. Collectively, our findings reveal that the neddylation pathway not only regulates hormonal perception and CO distribution but is also, directly or indirectly, a major limiting pathway of TE DNA methylation in somatic cells. |
Start Year | 2019 |
Description | Elsoms |
Organisation | Elsoms Seeds |
Country | United Kingdom |
Sector | Private |
PI Contribution | We have collaborated with Elsoms Seeds company to extend our work into Brassica napus. |
Collaborator Contribution | Elsoms Seeds produced double haploid Brasscia napus lines for us. |
Impact | Too early to say |
Start Year | 2019 |
Description | Communication with Elsoms Seeds company |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Industry/Business |
Results and Impact | I and Rachel Wells from JIC visited Elsoms Seeds company to discuss our work, the need of plant breeders, and potential future collaborations. As a result, we developed a collaboration working on Brassica napus, and are now evaluating the possibility of setting up transgenic work in Elsoms. |
Year(s) Of Engagement Activity | 2019 |
Description | Interview about career pathways in science |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | In an interview filmed by the Communications Team at JIC, I talked about my career path and experiences, mainly targetting young people interested in science. The video was released on the International Women's Day in 2022, on JIC website (and Twitter) and YouTube. |
Year(s) Of Engagement Activity | 2022 |
URL | https://www.jic.ac.uk/blog/career-pathways-in-science/ |