Characterisation of the Cf-Ecp2 gene encoding for recognition of the conserved fungal effector Ecp2 in Solanum pimpinellifolium and Nicotiana paniculata

Mccann, Lucy (2016) Characterisation of the Cf-Ecp2 gene encoding for recognition of the conserved fungal effector Ecp2 in Solanum pimpinellifolium and Nicotiana paniculata. Doctoral thesis, University of East Anglia.

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Abstract

Members of the Capnodiales class of fungi have evolved contrasting lifestyles on plants,
ranging from biotrophy, through to endotrophy and necrotrophy. Many of these fungi
contain homologs of the effector protein called Ecp2. The ‘currant’ tomato (Solanum
pimpinellifolium) resistance (R) gene Cf-Ecp2 recognises Ecp2 produced by the
pathogenic fungus, Cladosporium fulvum. In this study, Cf-Ecp2 was fine-mapped to the
Orion locus, which contains eight Homologs of Cladosporium resistance gene Cf-9 (Hcr9s),
four of which share 100% sequence identity within their open reading frame. The Cf-Ecp2
locus exemplifies the complex nature of many R gene loci brought about by successive
rounds of tandem duplication. This extensive duplication renders R gene loci complex
and difficult to resolve. As a consequence, the sequencing of a BAC minimal tiling path
across the Cf-Ecp2 locus required use of both short read and long read sequencing
technologies, with MinION providing vital scaffolding reads. A transposon mutagenesis
experiment generated two deletion mutants. The mutants had lost the ability to
recognise Ecp2 along with the OR2A (2A) gene from the Cf-Ecp2 locus. Wild-type tomato
(Solanum lycopersicum) Cf0 stable transformants, overexpressing 2A via the cauliflower
mosaic virus 35S promoter, partially recapitulated the S. pimpinellifolium CfEcp2
phenotype. Lack of penetrance of the phenotype in the transgenic plants was attributed
to the functional interference of 2A overexpression. The non-host, Nicotiana paniculata
TW99, also recognises Ecp2 from C. fulvum. N. paniculata CfEcp2 was characterised for
its ability to recognise many homologs of Ecp2, including those from Mycosphaerella
fijiensis (causal agent of Black Sigatoka on banana) and the wilt-causing fungi, Fusarium
oxysporum and Verticillium dahliae. The ability of Cf-Ecp2 to code for the recognition of
an effector from many plant pathogens provides an exciting opportunity to engineer
resistance to such pathogens in important crops.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Jackie Webb
Date Deposited: 30 Nov 2016 14:37
Last Modified: 30 Nov 2016 14:37
URI: https://ueaeprints.uea.ac.uk/id/eprint/61545
DOI:

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