The Role of Aphid Cathepsin B in Virulence: Linking Oral Secretions to Host Protein Interactions

Seddon-Roberts, George (2025) The Role of Aphid Cathepsin B in Virulence: Linking Oral Secretions to Host Protein Interactions. Doctoral thesis, University of East Anglia.

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Abstract

The green peach aphid, Myzus persicae, is an extremely polyphagous hemipteran herbivore able to colonise plants from over 40 plant families. This insect causes significant agricultural losses, both directly by causing mechanical damage during feeding, and indirectly via transmission of over 100 plant viruses. One key to the extreme generalism of M. persicae is its deployment of oral secretions containing effector molecules that modulate basal plant processes.

This thesis focuses on identifying the origins of orally secreted M. persicae proteins. I developed organ-specific RNA-seq methods, and found members of a recently expanded clade of CathB cysteine proteases are most highly expressed in the M. persicae foregut, rather than the salivary glands. Previous studies by my host lab have shown that several CathB proteins, including CathB6, are effectors that promote aphid fecundity by recruiting the plant immune regulator EDS1 and its partners to p-bodies. This effect is inhibited by the Arabidopsis thaliana alpha-crystallin domain-containing protein ACD28.9.

I show that members of the Myzus-expanded CathB clade exhibit different affinities for A. thaliana ACD28.9 in yeast. CathB12, the closest paralog of CathB6, does not bind ACD28.9, despite only two diverging residues versus the ACD28.9-binding region of CathB6. Reciprocal residue swaps between CathB6 and CathB12 established that these residues are necessary for ACD28.9-driven rescue of CathB from p-bodies.

I also show that ACD28.9 belongs to a clade of ACD proteins significantly expanded in the order Brassicales, and that other A. thaliana ACD proteins in this clade also bind CathB6. Previously, work by my host lab determined that M. persicae CathB effector genes upregulate in aphids on two plant species in this order (Brassica rapa and A. thaliana), and downregulate on Solanales.

In summary, this work provides evidence that aphid CathB effectors and plant ACD proteins might be engaged in an evolutionary arms race.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Kitty Laine
Date Deposited:	06 May 2026 12:20
Last Modified:	06 May 2026 12:20
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102913
DOI:

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