The Generation Gap - Mechanisms of maternal control on grain
Lead Research Organisation:
James Hutton Institute
Department Name: Cell & Molecular Sciences
Abstract
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Technical Summary
This proposal investigates the contribution of pre- and post-fertilisation developmental events in maternal tissues to grain development in barley. We build on our recent discovery that two transcription factors in barley, HvAP2 and HvMADS29, control grain size and shape, and regulate the growth, differentiation and/or death of the hull and ovary tissues. Here, we will evaluate a potential mechanistic relationship of maternal regulators to coordinate tissue growth and survival in the grain.
We hypothesise that tissue transcriptomes will reflect this relationship and predict that these are responsive to regulation by HvAP2 and HvMADS29. To test this prediction we will define, for the first time, cell-specific transcriptomes within pre- and post-fertilisation cereal ovaries by single cell RNAseq (scRNAseq) and computational clustering to build cell populations with similar transcriptomic states and analyse how these states change over time and in response to loss of HvAP2 or HvMADS29 function. Furthermore, we will exploit a heat-inducible Cre-lox gene expression system to restore maternal regulators at specific developmental stages in loss of function mutants to assess responses in the grain size and shape and in cell-specific transcriptomes.
We also hypothesise that grain shape differences in wild compared to cultivated barley may reflect altered maternal tissue developmental processes. We will explore this idea by characterising maternal tissue development by histology approaches followed by scRNAseq on wild barley tissues. Comparative analyses with cultivated grain will reveal conserved and diverged developmental transcriptomic trajectories which may contribute to differences in wild compared to cultivated grain. We will select diverse allelic variation in wild maternal tissue regulators and assess their function in cultivated germplasm by accelerating introgression lines.
We hypothesise that tissue transcriptomes will reflect this relationship and predict that these are responsive to regulation by HvAP2 and HvMADS29. To test this prediction we will define, for the first time, cell-specific transcriptomes within pre- and post-fertilisation cereal ovaries by single cell RNAseq (scRNAseq) and computational clustering to build cell populations with similar transcriptomic states and analyse how these states change over time and in response to loss of HvAP2 or HvMADS29 function. Furthermore, we will exploit a heat-inducible Cre-lox gene expression system to restore maternal regulators at specific developmental stages in loss of function mutants to assess responses in the grain size and shape and in cell-specific transcriptomes.
We also hypothesise that grain shape differences in wild compared to cultivated barley may reflect altered maternal tissue developmental processes. We will explore this idea by characterising maternal tissue development by histology approaches followed by scRNAseq on wild barley tissues. Comparative analyses with cultivated grain will reveal conserved and diverged developmental transcriptomic trajectories which may contribute to differences in wild compared to cultivated grain. We will select diverse allelic variation in wild maternal tissue regulators and assess their function in cultivated germplasm by accelerating introgression lines.
Organisations
| Description | The work on this project is headed by Sarah McKim (University of Dundee) with this award to the James Hutton Institute as a subsidiary award to allow for the development of specific barley material etc, One of our research's main objectives was to define gene expression during grain formation and develop computational pipelines for these data. Following multiple trials we pursued single nuclei sequencing (snRNAseq), a reliable method for recalcitrant tissues. We adapted this technique for developing barley grain. We now have datasets and an established computational pipeline. We are currently analysing these data. We expect to complement this work with spatial validation during the last part of this grant. This will provide the most precise understanding of gene expression during grain formation in a temperate cereal. Other objectives included identification of the causal genes for a selection grain mutants . We have now identified two candidate genes as encoding proteins involved in trafficking, suggesting a new developmental role for these regulators, with final validation experiments in process. We also discovered a new hormonal control of maternal tissue growth during grain development. A final objective was to understand gene expression in wild barley and assess the influence of wild vs cultivated maternal regulators on grain formation. We plan final experiments to address wild barley grain transcriptomes and have conclusively that maternal control is the dominant mechanism regulating grain parameters regardless of wild versus domesticated origin. We also showed that variation in key maternal regulators do not explain divergence between wild and domesticated barley. We since exploited powerful genetic resources which show a promising genetic element controlling grain size from wild germplasm. We have narrowed the region to a relatively small interval and hope to identify the underling gene going forward. Taken together, we are making excellent progress and are broadly meeting our original aims |
| Exploitation Route | The findings of this project are already influencing other work on barley, in particular work involving the use of wild barley. The understanding of the control of grain size in this small grain cereal has clear longer-term implications for breeding and ultimately end user industries. This understanding is already helping with the framing of research work with barley's wild relatives including ongoing projects funded by the BBSRC. The utilisation of this largely untapped source of genetic variation has the potential to fundamentally broaden the genetic base of the crop but there are barriers to its use. Having a clearer understanding of the particular mechanisms and genes involved in differences between cultivated and wild barley will allow the unpicking of the results of domestication and potentially allow a targeted improvement of grain size in this crop. |
| Sectors | Agriculture Food and Drink |
| Description | Invited presentation at Association of Applied Biologists (AAB) meeting on 'Cereal Quality for Sustainable Production and Human Health' |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | The mini-conference brought together researchers and students working in different areas of sustaining food chains to help improve human health, as well as meet processor and consumer expectations whilst under increasing environmental pressures. This enabled considerable discussion and drew out comparisons between crops/cropping systems. |
| Year(s) Of Engagement Activity | 2024 |