Cross-regulation of receptor signalling to maintain the balance between growth and immunity.

Dräger, Markus (2024) Cross-regulation of receptor signalling to maintain the balance between growth and immunity. Doctoral thesis, University of East Anglia.

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Abstract

Plant cells continuously perceive and respond to diverse extracellular signals. Among these signals are small peptides that are secreted by the plant and perceived by specialised cell-surface receptors. Plants secrete a vast diversity of these peptides which play critical roles in fine-tuning and facilitating cellular responses to biotic and abiotic stimuli and are therefore essential for environmental adaptation.

The receptor kinase PHYTOSULFOKINE RECEPTOR 1 (PSKR1) perceives the peptide PHYTOSULFOKINE (PSK) to modulate plant growth, immunity, and microbiome composition. To understand the molecular mechanisms downstream of PSKR1, I use Affinity Purification-Mass Spectrometry (AP-MS) to identify novel signalling components, including MITOGEN-ACTIVATED KINASE KINASE KINASE 7 (MKKK7). Functional analysis using mkkk7 mutants generated by CRISPR-Cas9 reveals that MKKK7 regulates specific PSK-induced responses, such as protoplast expansion and nutrient-related gene expression, while growth promotion and suppression of immunity are unaffected.

MKKK7 was previously shown to act downstream of the immune receptor FLAGELLIN SENSITIVE 2 (FLS2), but its mode of action remained unexplored. Here, I show that MKKK7 likely acts partially redundantly with its closely related homologue MKKK6 in Arabidopsis, with double mutants showing severe developmental defects. I confirm that the perception of PATHOGEN-ASSOCIATED MOLECULAR PATTERN (PAMP) flg22 by FLS2 triggers MKKK7 phosphorylation and show in addition that the intracellular immune kinase BOTRYTIS INSENSITIVE 1 (BIK1) phosphorylates MKKK7. Lastly, I show that MKKK7 is an active kinase that triggers cell death when overexpressed in Nicotiana benthamiana, highlighting its role in plant growth and immunity.

When considered together, the complex relationship of MKKK7 with both the FLS2 immune- and PSKR1 growth-signalling pathways provides new insights into the mechanisms that balance plant growth and immunity. Understanding receptor kinase signalling at the molecular level will help to inform strategies to shift the balance in favour of plants that exhibit both robust growth and enhanced immunity.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > The Sainsbury Laboratory
Depositing User:	James Tweddle
Date Deposited:	18 Feb 2025 12:52
Last Modified:	18 Feb 2025 12:52
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98534
DOI:

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