Specific Hypersensitive Response–Associated Recognition of New Apoplastic Effectors from Cladosporium fulvum in Wild Tomato

Abstract

Tomato leaf mold disease is caused by the biotrophic fungus Cladosporium fulvum. During infection, C. fulvum produces extracellular small secreted protein (SSP) effectors that function to promote colonization of the leaf apoplast. Resistance to the disease is governed by Cf immune receptor genes that encode receptor-like proteins (RLPs). These RLPs recognize specific SSP effectors to initiate a hypersensitive response (HR) that renders the pathogen avirulent. C. fulvum strains capable of overcoming one or more of all cloned Cf genes have now emerged. To combat these strains, new Cf genes are required. An effectoromics approach was employed to identify wild tomato accessions carrying new Cf genes. Proteomics and transcriptome sequencing were first used to identify 70 apoplastic in planta-induced C. fulvum SSPs. Based on sequence homology, 61 of these SSPs were novel or lacked known functional domains. Seven, however, had predicted structural homology to antimicrobial proteins, suggesting a possible role in mediating antagonistic microbe-microbe interactions in planta. Wild tomato accessions were then screened for HR-associated recognition of 41 SSPs, using the Potato virus X-based transient expression system. Nine SSPs were recognized by one or more accessions, suggesting that these plants carry new Cf genes available for incorporation into cultivated tomato.Leaf mold disease of tomato (Solanum lycopersicum) is caused by the biotrophic Dothideomycete fungal pathogen Cladosporium fulvum (syn. Passalora fulva and Fulvia fulva) (Thomma et al. 2005). The fungus likely originated in South America, the center of origin for tomato (Jenkins 1948), with Nucleotide sequence data is available in the GenBank database under the following accession numbers: Ecp6, KX943112; Ecp7, KX943113; Ecp8, KX943038; Ecp9-1, KX943041; Ecp9-2, KX943114; Ecp9-3, KX943115; Ecp9-4, KX943116; Ecp9-5, KX943117; Ecp9-6, KX943118; Ecp9-7, KX943119; Ecp9-8, KX943120; Ecp9-9, KX943081; Ecp10-1, KX943046; Ecp10-2, KX943063; Ecp10-3, KX943121; Ecp11-1, KX943050; Ecp12, KX943058; Ecp13, KX943065; Ecp14-1, KX943087; Ecp14-2, KX943122; Ecp15, KX943091; Ecp16, KX943080; Ecp17, KX943051; Ecp18, KX943035; Ecp19-1, KX943036; Ecp19-2, KX943048; Ecp20-1, KX943037; Ecp20-2, KX943057; Ecp20-3, KX943096; Ecp21-1, KX943039; Ecp22, KX943040; Ecp23, KX943044; Ecp24-1, KX943045; Ecp24-2, KX943094; Ecp25, KX943047; Ecp26, KX943052; Ecp27, KX943054; Ecp28-1, KX943056; Ecp28-2, KX943088; Ecp28-3, KX943090; Ecp29, KX943103; Ecp30, KX943076; Ecp31, KX943059; Ecp32-1, KX943062; Ecp32-2, KX943101; Ecp33, KX943066; Ecp34, KX943067; Ecp35, KX943068; Ecp36-1, KX943069; Ecp37, KX943072; Ecp38, KX943073; Ecp39, KX943074; Ecp40, KX943079; Ecp41, KX943082; Ecp42, KX943083; Ecp43-1, KX943089; Ecp44, KX943092; Ecp45, KX943093; Ecp46, KX943095; Ecp47, KX943097; Ecp48, KX943098; Ecp49-1, KX943099; Ecp50-1, KX943100; Ecp51, KX943102; Ecp52, KX943104; Ecp53-1, KX943105; Ecp54-1, KX943107; Ecp55, KX943108; Ecp56, KX943110; Ecp57-1,

Conservation and expansion of a necrosis‐inducing small secreted protein family from host‐variable phytopathogens of the Sclerotiniaceae

“…The cysteine residues within fungal effector proteins are proposed to form disulphide bonds, which help maintain protein stability within plant tissue (Joosten et al , ; Luderer et al , ). More recently, effector screening strategies have begun to incorporate complex information, including temporal and tissue‐specific gene expression patterns, evidence for positive selection, proteomics, three‐dimensional protein structure prediction, and comparative secretome analyses (Pedersen et al , ; Guyon et al , ; de Guillen et al , ; Lo Presti et al , ; Sperschneider et al , ; Heard et al , ; Mesarich et al , ).…”

Comparative transcriptome analysis reveals the response mechanism of Cf-16-mediated resistance to Cladosporium fulvum infection in tomato

“…Incompatible interactions (chlorosis) lead to the hypersensitive response (HR) when plants resist pathogens; compatible interactions occur when the pathogens can grow and ramify, causing necrosis in infected cells [14][15][16][17]. The tomato-C. fulvum interaction follows a typical gene-for-gene relationship, and the products of C. fulvum-resistance genes (Cf genes) in tomato specifically recognize the products encoded by the AVR genes in C. fulvum, leading to HR [18,19]. At least 24 Cf genes have been reported since the discovery of the Cf-1 gene in the 1930s [20,21], and these genes have been introduced into cultivated tomatoes [22][23][24][25][26][27][28][29][30].…”

Population studies of the wild tomato species Solanum chilense reveal geographically structured major gene-mediated pathogen resistance

“…Yet, our findings show that northern and central populations of S. chilense do possess resistance against C. fulvum race 5. Our apoplastic extract contains at least 70 secreted effectors, which are all potential Avrs (Mesarich et al , 2017). The chance of losing recognition for all of these effectors by mutations in the matching receptors is highly unlikely, thus hinting at general differences in the regulation of Avr recognition.…”

“…Appreciating the important roles of these Cf genes and their assumed role in co-evolution between wild tomato and native C. fulvum , it is surprising that only a few studies have sought to investigate Cf gene diversity. An effectoromics approach was exploited by Mesarich et al (2017), to identify plants carrying novel Cf genes to be potentially used in plant breeding programs in the future. Studies have shown that in S. pimpinellifolium several putative homologs are present, but their function remains unknown (Caicedo et al ., 2004; Caicedo, 2008).…”