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Signalling Sex in Plants: The Role of Peptide Signals and the Cell Wall in Fertilisation

Reference	BB/W013754/1
Principal Investigator / Supervisor	Dr Lisa Megan Smith
Co-Investigators / Co-Supervisors	Professor Andrew James Fleming
Institution	University of Sheffield
Department	School of Biosciences
Funding type	Research
Value (£)	480,363
Status	Current
Type	Research Grant
Start date	01/11/2022
End date	31/10/2025
Duration	36 months

Abstract

Fertilisation is a useful model for cell-to-cell signalling due to the strict spatial and temporal resolution of events. The genetic resources of Arabidopsis allow faster generation of mechanistic knowledge of such complex systems before translation into crops where reproduction is sensitive to climatic extremes (e.g. soft fruits). At Sheffield, we have recently expanded the number of CrRLK1L receptor kinases linked to female gametophyte signalling during pollen tube reception from the founding member of FERONIA to include HERK1 and ANJEA. Ligands for the three ovule-expressed receptor kinases are expected to be rapid alkalisation factor (RALF) peptides, as RALF peptides are bound by FERONIA and ANJEA during pollen hydration on the stigma, and by related CrRLK1L receptors during pollen tube growth. Having identified the CrRLK1L receptor kinases that are critical in the female gametophyte during the pollen tube reception step of fertilisation, we now aim to further elucidate peptide-receptor signalling and its consequences for cell wall composition during this key step of plant reproduction. In an international collaboration (thus addressing the BBSRC priority of 'International partnerships'), we will: identify and verify the peptide signals perceived by receptor kinases in the ovule during pollen tube reception; map and functionally test changes in ovule cell wall composition in response to pollen tube reception that are dependent on CrRLK1L receptors; identify the peptides signalling from the ovule to the pollen tube during reception; and map and functionally test subsequent changes in cell wall composition in the pollen tube. Together these approaches will make a step change in our understanding of peptide-receptor-cell wall signalling, using the fundamental biological process of fertilisation as a model. The project will also deliver a high level of technical training to a post-doctoral research associate and a technician.

Summary

Plant reproduction underpins seed production and is central to food security, yet our understanding of the molecular process by which ovules (the female gametes) are fertilised by pollen (the male gametes) remains incomplete. Fertilisation involves tightly regulated communication between the gametes to ensure that the pollen tube reaches the ovule and releases the sperm cells at the correct position within the ovule. At the core of this molecular conversation is a group of related receptor kinases which span the cell membrane to detect small molecules outside the cell. Signal detection by these receptors is translated into an appropriate cell response via varied downstream events. We know that this family of receptors binds small proteins (peptides) as external cell signals, however the identity of the peptides that pass between the pollen tube and ovules during pollen tube reception is unknown. Downstream events likely include changes in cell wall composition to allow degeneration of a specialised synergid cell at the entrance of the ovule, and burst of the pollen tube within the ovule, but functional data to support this idea is limited, and the range of cell wall changes unclear. Peptide-receptor-cell wall signalling during pollen tube reception is, thus, poorly understood. We will address a number of questions regarding signalling from the pollen tube to the ovule and vice versa in this project using Arabidopsis: 1) which peptides are perceived by the three receptor kinases at the ovule?; 2) which ovule cell wall composition changes during fertilisation are important and which receptors mediate these changes?; 3) are similar peptide signals passed back to the pollen tube from the ovule?; and 4) do they also result in cell wall composition changes required for fertilisation? These questions lead directly to the objectives of the project. Firstly, we will use an assay for receptor signalling in living ovules and test responses to a panel of synthesised ovule andpollen tube peptides to identify which peptides and receptors interact. Secondly, we will produce an atlas of cell well composition in ovules during pollen tube reception in normal plants and mutants lacking the key ovule receptors. Genetic and biochemical techniques will be used to test the functional significance of the interaction of peptides with the ovule receptors, and importance of the cell wall changes for fertilisation. Thirdly, we will then test if similar peptides signal from the ovule back to pollen tube receptors, and fourthly, what changes are seen in pollen tube cell wall composition during fertilisation, following up with genetic and biochemical characterisation of these functions. We will therefore make a significant advance in our understanding of the fundamental process of plant fertilisation, linking signal transduction to altered cell wall composition, and providing novel insight into how signalling controls gamete responses. Longer term, the agricultural industry will benefit from greater understanding of the mechanism behind plant fertilisation, a process important for all our major crops. Due to evolutionary conservation of this fundamental process, knowledge of how fertilisation occurs in a model plant can inform attempts to improve fertilisation (and yield) in crops. This is particularly relevant in the context of the ongoing climate emergency, with more extreme temperature events affecting fertilisation and thus yield. The knowledge gained will contribute to efforts to breed climate ready crops. Beneficiaries of this project include the scientific community who will gain from expanded understanding of plant signalling, using fertilisation as a tractable model system. A post-doctoral research associate and technician will benefit from training in genetics, biochemistry, and molecular, developmental and cell biology. Finally, by supporting a collaboration with Switzerland, the project will strengthen international ties.

Committee	Research Committee B (Plants, microbes, food & sustainability)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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