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Evolution and Function of Receptor-like Kinases in Arbuscular Mycorrhizal Symbiosis

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Chiu, Chai Hao 


Evolution of the nutritional mutualism between plants and arbuscular mycorrhizal (AM) fungi was crucial to evolution of life, as it enabled the conquest of the green lineage and its ecosystem on land. Today, apart from AM fungi, plants co-exist with a plethora of micro-organisms, and exactly how the plant immune system balances the need for defence against detrimental micro-organisms and beneficial ones such as AM fungi remains enigmatic. This work characterised plant plasma membrane receptors that perceive microbial carbohydrate patterns, and how they bring about cellular and developmental changes. To understand the origins of the Lysin-motif (LysM) receptor-like kinases (RLKs) and Symbiosis Receptor Kinase (SYMRK), comprehensive phylogenomic analyses of these receptors in more than a hundred plant genomes revealed their deep origins in green algae. I then defined the major clades of LysM-RLKs, their correlation with plant symbiotic capabilities, how the pseudokinases have diversified and refined, and how the ancestral LysM-RLK gave rise to the repertoire in extant land plants. Independent events involving domain fusions of LysM with kinase domains in the plant kingdom and beyond demonstrate how modularity of protein domains enable genetic innovations in the tree of life.

A clearly defined receptor phylogeny also enabled systematic genetic dissection of the RLKs. Functions of four different receptor clades were carefully analysed in rice using single and double mutants. Careful assessment of AM colonisation in these mutants reveal chitin and lipochito-oligosaccharides as redundant signals, perceived by an equally redundant set of RLKs, as well as a symbiosis-specific receptor that represents a second checkpoint of symbiotic scrutiny – confirming insights from phylogenomic analyses. Perception of AM fungi also result in plants producing more lateral roots, a response observed for decades. Here, molecular mechanisms of this developmental response are elucidated, where general perception of chitin-derived molecules through LysM receptors and SYMRK activate lateral organ production. This response is also conserved in non-AM hosts, revealing the existence of an ancestral signalling function of these RLKs in shaping plant development – which may have been recruited in the evolution of nitrogen fixing root-nodules. Transgenic lines containing tagged-RLKs were also characterised, paving the way for future biochemical experiments to understand how the receptor complexes activate downstream signalling components for their biological functions.





Paszkowski, Uta


arbuscular mycorrhiza, kinases, plants, receptors, root development, symbiosis


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Gates Cambridge Trust PhD Scholarship