Bioinformatic analysis and functional characterization of CFEM proteins in Setosphaeria turcica

Abstract

Common in Fungal Extracellular Membrane (CFEM) domains are uniquely found in fungal extracellular membrane proteins which are important for pathogens. This study identified 13 StCFEM proteins in the genome of Setosphaeria turcica, the hemibiotrophic fungus that causes northern corn leaf blight. Sequence alignment and WebLogo analysis of their CFEM domains indicated that the amino acids were highly conserved and that, with the exception of StCFEM1, 2, 3, and 6, they contained eight cysteines. Phylogenic analysis suggested that these 13 proteins (StCFEM1–13) could be divided into 2 clades based on the presence of the trans-membrane domain. Six StCFEM proteins with a signal peptide and without a trans-membrane domain were considered as candidate effector proteins. The CFEM domain in the candidate effector proteins could form a helical-basket structure homologous to Csa2 in Candida albicans. Transcriptome analysis suggested that the 13 genes were expressed during fungal infection and a yeast secretion assay revealed that these candidate effectors were secreted proteins. It was also found that StCFEM3, 4, and 5 couldn't affect BAX/INF1-induced programmed cell death (PCD) in Nicotiana benthamiana and while StCFEM12 could suppress INF1-induced PCD, it showed no effect on BAX-induced PCD. This study found that there were 13 members of the S. turcica CFEM protein family and that StCFEM12 was a candidate effector. This study laid the foundation for illustrating the roles of CFEM proteins during the pathogenic processes of phytopathogens.