| NSF Org: |
DEB Division Of Environmental Biology |
| Recipient: |
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| Initial Amendment Date: | April 9, 2015 |
| Latest Amendment Date: | April 9, 2015 |
| Award Number: | 1500654 |
| Award Instrument: | Standard Grant |
| Program Manager: |
George Gilchrist
DEB Division Of Environmental Biology BIO Directorate for Biological Sciences |
| Start Date: | June 1, 2015 |
| End Date: | November 30, 2016 (Estimated) |
| Total Intended Award Amount: | $20,129.00 |
| Total Awarded Amount to Date: | $20,129.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
107 S INDIANA AVE BLOOMINGTON IN US 47405-7000 (317)278-3473 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1001 E 3RD ST Bloomington IN US 47405-7005 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | EVOLUTIONARY GENETICS |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.074 |
ABSTRACT
This study aims to understand gamete recognition (chemical cues used by male and female gametes to recognize and attract each other) as a mechanism of sexual reproduction, and how it acts to prevent reproductive events between different species. This work uses the domesticated tomato and its twelve diverse wild species relatives, which vary in many reproductive and functional traits. The project will first identify the chemical signal derived from the female gamete that attracts the male gamete within species. Second, it will characterize variation in this signal across species and connect this variation to previously observed reduced gamete attraction between species. In addition to understanding molecular mechanisms of normal and attenuated reproductive function, these data could aid in overcoming breeding barriers between domesticated tomato and its genetically diverse wild relatives. This project will include research by undergraduates from underrepresented groups and potential insights of agricultural importance for crop breeding.
To identify the female gamete-derived chemoattractant and its specific tissue of origin, this project will use high depth nucleotide sequencing technologies (RNA-seq) for tissue specific expression analysis. It will assess molecular divergence of this signaling protein via variation in sequence and/or expression across 13 closely related species. These combined approaches will explicitly link patterns of molecular expression and DNA variation to functional divergence in reproductive behaviors. Although many studies have demonstrated that species show reduced sexual compatibility, the underlying molecular mechanisms are generally unknown. Together, this research will provide an unprecedented opportunity to examine the patterns and consequences of evolutionary changes in a reproductive molecule, including for the development of new species.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
This study examined molecules involved in gamete recognition and attraction—the mechanism by which male and female gametes recognize and are guided to each other via chemical cues—in an economically important plant group. Gamete recognition is required for successful sexual reproduction (fertilization), and can also act to prevent reproductive events between different species. However, the specific molecules involved in gamete recognition and attraction are known in very few species, especially among angiosperms (flowering plants). This work used 12 species of wild tomato—that display broad reproductive and ecological diversity, as well as their close relative—the domesticated tomato, to identify a signal molecule involved in gamete attraction prior to fertilization in this plant group. This ‘chemoattractant’ is secreted from the ovule (the female tissue that contains the egg cell) and acts as a directional signal for the growing pollen tubes (which contain the male sperm).
First, the research used ‘next-generation’ sequencing techniques (“RNAseq”) to generate DNA profiles of all genes that are actively expressed in mature unfertilized ovules (their “transcriptome”), from populations of all 13 tomato species. Computational assembly, analysis, and comparison of each transcriptome, was used to identify the most abundantly expressed genes in this tissue. Based on very high expression levels and structural features (short cysteine-rich peptides with secretion signals), two genes were identified for further analysis, in conjunction with data on patterns of gamete attraction within and between species.
Using variation in the DNA sequences at each gene, the molecular variation and divergence of each was examined across all 13 closely related tomato species. These data were used to assess the number and location of sequence differences between species, including between species that do and do not show reductions in gamete chemoattraction. Only one of the genes had protein-changing differences between the species that show significant reductions in interspecific chemoattraction, and rates of protein-changing molecular evolution that are higher than the genome-wide average. Using a classical genetic approach based on hybrid lines made between species, the chromosomal region containing this gene was confirmed to significantly influence chemoattraction behavior between ovules and pollen tubes, among different species. Together, these data suggest that this gene codes for an ovule-secreted chemoattractant that contributes to successful fertilization within tomato species, and reduced rates of fertilization between some of these species.
This study therefore explicitly linked patterns of molecular expression at a plausible candidate gene with divergence in reproductive behaviors in a diverse plant group. These data are valuable for understanding general mechanisms of reproductive signaling, and molecular variation that leads to attenuated reproductive compatibility between divergent genomes. In addition, they can be used to better understand the reproductive biology of fertilization in an economically important plant group, including in the domesticated tomato. This research also contributed directly to training and professional development in the STEM disciplines of one female graduate student and two female undergraduate students, in techniques for plant breeding, and in bioinformatics required for the generation, handling, analysis, and interpretation of large gene expression datasets.
Last Modified: 03/28/2017
Modified by: Leonie C Moyle
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