Evolution of nuclear calcium signalling in land plants

Lam, Ho Ching Anson (2024) Evolution of nuclear calcium signalling in land plants. Doctoral thesis, University of East Anglia.

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Abstract

Approximately 80% of land plants form mutually beneficial association with arbuscular mycorrhizal (AM) fungi. AM symbiosis can improve the acquisition of nutrients of the host plants, and plants provide fixed carbon to the AM fungi. The evolution of AM symbiosis coincides with the appearance of early land plants that first colonized land over 450 million years ago, suggesting that the evolution of AM symbiosis was an important adaptation for plants in terrestrial environments. The formation of AM and another intracellular symbiosis, root nodulation, depends on the common symbiosis signalling pathway. Perception of chitooligosaccharide-based molecules from symbionts activates nuclear calcium oscillation in the root, involving ion channels DOES NOT MAKE INFECTIONS1 (DMI1) and CYCLIC NUCLEOTIDE-GATED CHANNEL 15 (CNGC15). Nuclear calcium oscillation is essential for endosymbiosis in angiosperms, but given that early land plants lacked roots, whether it is also required for AM in non-flowering plants is unknown.

Addressing this question, this work found that AM germinating spore exudate (GSE) activates nuclear calcium oscillation in rhizoids of the liverwort Marchantia paleacea, and this is dependent on the nuclear localized MpaDMI1. In M. paleacea, AM fungal hyphae infect the rhizoids, and form arbuscules in the thalli. However, unlike angiosperms, nuclear calcium signalling is only required for the thalli colonization but not rhizoid infections. Unexpectedly, MpaDMI1 cannot transcomplement Mtdmi1 mutants in AM and root nodulation, and the mechanism of regulating DMI1 has diverged between M. paleacea and the legume Medicago truncatula. A key amino acid residue L503 is essential to sustain MtDMI1 in an inactive state. Reverse genetics has also demonstrated that MpaCNGCs have a conserved role in AM symbiosis and development in M. paleacea.

This thesis provides insights into the functional evolution of nuclear calcium signalling between liverworts and flowering plants, and opens new avenues of research into the mechanism of endosymbiosis signalling.

Keywords: Evolution, Arbuscular mycorrhizae, Root nodule, Nuclear calcium signalling, DMI1, CNGC, Marchantia paleacea

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	08 Jan 2025 11:52
Last Modified:	08 Jan 2025 11:52
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98116
DOI:

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