New insights into the evolution of subtilisin-like serine protease genes in Pezizomycotina.
BACKGROUND
Subtilisin-like serine proteases play an important role in pathogenic fungi during the penetration and colonization of their hosts. In this study, we perform an evolutionary analysis of the subtilisin-like serine protease genes of subphylum Pezizomycotina to find if there are similar pathogenic mechanisms among the pathogenic fungi with different life styles, which utilize subtilisin-like serine proteases as virulence factors. Within Pezizomycotina, nematode-trapping fungi are unique because they capture soil nematodes using specialized trapping devices. Increasing evidence suggests subtilisin-like serine proteases from nematode-trapping fungi are involved in the penetration and digestion of nematode cuticles. Here we also conduct positive selection analysis on the subtilisin-like serine protease genes from nematode-trapping fungi.


RESULTS
Phylogenetic analysis of 189 subtilisin-like serine protease genes from Pezizomycotina suggests five strongly-supported monophyletic clades. The subtilisin-like serine protease genes previously identified or presumed as endocellular proteases were clustered into one clade and diverged the earliest in the phylogeny. In addition, the cuticle-degrading protease genes from entomopathogenic and nematode-parasitic fungi were clustered together, indicating that they might have overlapping pathogenic mechanisms against insects and nematodes. Our experimental bioassays supported this conclusion. Interestingly, although they both function as cuticle-degrading proteases, the subtilisin-like serine protease genes from nematode-trapping fungi and nematode-parasitic fungi were not grouped together in the phylogenetic tree. Our evolutionary analysis revealed evidence for positive selection on the subtilisin-like serine protease genes of the nematode-trapping fungi.


CONCLUSIONS
Our study provides new insights into the evolution of subtilisin-like serine protease genes in Pezizomycotina. Pezizomycotina subtilisins most likely evolved from endocellular to extracellular proteases. The entomopathogenic and nematode-parasitic fungi likely share similar properties in parasitism. In addition, our data provided better understanding about the duplications and subsequent functional divergence of subtilisin-like serine protease genes in Pezizomycotina. The evidence of positive selection detected in the subtilisin-like serine protease genes of nematode-trapping fungi in the present study suggests that the subtilisin-like serine proteases may have played important roles during the evolution of pathogenicity of nematode-trapping fungi against nematodes.
Li
Juan
J
Laboratory for Conservation and Utilization of Bio-resources, and Key Laboratory for Microbial Resources of the Ministry of Education, Yunnan University, Kunming, 650091, PR China.
Yu
Li
L
Yang
Jinkui
J
Dong
Linqian
L
Tian
Baoyu
B
Yu
Zefen
Z
Liang
Lianming
L
Zhang
Ying
Y
Wang
Xu
X
Zhang
Keqin
K
D000595:Amino Acid Sequence; D000818:Animals; D001203:Ascomycota / Q000201:enzymology / Q000235:genetics*; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009348:Nematoda / Q000382:microbiology; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013381:Subtilisins / Q000235:genetics*
D004271:DNA, Fungal; D005656:Fungal Proteins; D013381:Subtilisins