Abstract
Fungal plant pathogens produce secreted proteins adapted to function outside fungal cells to facilitate colonization of their hosts. In many cases such as for fungi from the Sclerotiniaceae family the repertoire and function of secreted proteins remains elusive. In the Sclerotiniaceae, whereas Sclerotinia sclerotiorum and Botrytis cinerea are cosmopolitan broad host-range plant pathogens, Sclerotinia borealis has a psychrophilic lifestyle with a low optimal growth temperature, a narrow host range and geographic distribution. To spread successfully, S. borealis must synthesize proteins adapted to function in its specific environment. The search for signatures of adaptation to S. borealis lifestyle may therefore help revealing proteins critical for colonization of the environment by Sclerotiniaceae fungi. Here, we analyzed amino acids usage and intrinsic protein disorder in alignments of groups of orthologous proteins from the three Sclerotiniaceae species. We found that enrichment in Thr, depletion in Glu and Lys, and low disorder frequency in hot loops are significantly associated with S. borealis proteins. We designed an index to report bias in these properties and found that high index proteins were enriched among secreted proteins in the three Sclerotiniaceae fungi. High index proteins were also enriched in function associated with plant colonization in S. borealis, and in in planta-induced genes in S. sclerotiorum. We highlight a novel putative antifreeze protein and a novel putative lytic polysaccharide monooxygenase identified through our pipeline as candidate proteins involved in colonization of the environment. Our findings suggest that similar protein signatures associate with S. borealis lifestyle and with secretion in the Sclerotiniaceae. These signatures may be useful for identifying proteins of interest as targets for the management of plant diseases.
Highlights
Fungi from the Sclerotiniaceae family include several devastating plant pathogens with a broad host range
To test whether S. borealis proteins have a distinctive pattern of amino acid usage and disorder compared to S. sclerotiorum and B. cinerea proteins, we designed a bioinformatics pipeline to process complete proteomes deduced from the whole genome sequences of these three fungal pathogens (Figure 2) (Amselem et al, 2011; Mardanov et al, 2014a)
Secreted proteins account for 6.5% of total proteome in S. borealis, 4.5% in S. sclerotiorum and 4.5% in B. cinerea, the proportion of secreted proteins among those with sTEKhot > 1.5 raised to 76.9% (206 out of 268) in S. borealis, 68.2% (182 out of 267) in S. sclerotiorum and 65.0% (206 out of 317) in B. cinerea, representing ∼13.6 fold enrichment in secreted proteins (Figure 6B). These results suggest that intrinsic protein disorder and amino acid usage patterns associated with S. borealis lifestyle and secretion are largely overlapping in the Sclerotiniaceae
Summary
Fungi from the Sclerotiniaceae family include several devastating plant pathogens with a broad host range. The repertoire of molecules contributing to the ability of plant pathogenic fungi, such as fungi from the Sclerotiniaceae family, to colonize a wide range of hosts and environments remains elusive. Fungal pathogens use molecules designated as effectors to manipulate host cells and achieve successful infection. Their activities include the inactivation of plant defenses, interference with plant hormone balance, or dismantling of the plant cell. Effector detection in fungal pathogens relies largely on specific host responses revealing effector recognition, and bioinformatics approaches based on whole genome sequences and deduced protein repertoires remain challenging (Sperschneider et al, 2015). In the Ascomycete genus Metarhizium, signatures of positive selection were observed less frequently in the genome of fungal pathogens
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
