Glycoside Hydrolase (GH) 45 and 5 Candidate Cellulases in Aphelenchoides besseyi Isolated from Bird’s-Nest Fern

Abstract

Five Aphelenchoides besseyi isolates collected from bird’s-nest ferns or rice possess different parasitic capacities in bird’s-nest fern. Two different glycoside hydrolase (GH) 45 genes were identified in the fern isolates, and only one was found in the rice isolates. A Abe GH5-1 gene containing an SCP-like family domain was found only in the fern isolates. Abe GH5-1 gene has five introns suggesting a eukaryotic origin. A maximum likelihood phylogeny revealed that Abe GH5-1 is part of the nematode monophyletic group that can be clearly distinguished from those of other eukaryotic and bacterial GH5 sequences with high bootstrap support values. The fern A. besseyi isolates were the first parasitic plant nematode found to possess both GH5 and GH45 genes. Surveying the genome of the five A. besseyi isolates by Southern blotting using an 834 bp probe targeting the GH5 domain suggests the presence of at least two copies in the fern-origin isolates but none in the rice-origin isolates. The in situ hybridization shows that the Abe GH5-1 gene is expressed in the nematode ovary and testis. Our study provides insights into the diversity of GH in isolates of plant parasitic nematodes of different host origins.

Functional Variation of Two Novel Cellulases, Pv-eng-5 and Pv-eng-8, and the Heat Shock 90 Gene, Pv-hsp-90, in Pratylenchus vulnus and Their Expression in Response to Different Temperature Stress

“…Gene duplication along with single-nucleotide polymorphisms (SNPs) are major sources of functional diversification because the evolution of paralogs is strongly accelerated as duplication occurs. Phylogenetic analysis based on all GH5 catalytic cellulase domains of plant parasitic nematodes placed P. vulnus endoglucanases in three distinct groups (Figure 1), supporting the previous conclusions that in the early Pratylenchidae common ancestor, the HGT event was immediately followed by gene duplications, rapid gene turnover, and sequence diversification [34,36,37,38,39,40,41,53,54]. This evolutionary mechanism is known as subfunctionalization in which each duplicated gene maintains part of functions of the ancestral gene [55].…”

“…It is well known that the acquired genes before separation of the different nematode lineages underwent multiple duplications, thus forming multigene families. Then, after separation, the gene duplication process continued indipendently, leading to novel gene variants with diversification/specialization of function and selective expansion of some genes that are associated with the evolution of the parasitic life style [35,36,37,38,39,40,41]. HGT events of putative cellulases seems to be more frequent in plant parasitic nematodes than in any other trophic groups, but recently it has also been reported in necromenic nematodes belonging to Pristionchus genus [42].…”

Life-stage specific transcriptomes of a migratory endoparasitic plant nematode, Radopholus similis elucidate a different parasitic and life strategy of plant parasitic nematodes

“…No putative genes coding for cell wall modified enzymes in GH45 family was found in R. similis and other nematodes parasitizing plant underground tissue. At present, GH45 family genes are only reported in Aphelenchoidea nematodes for PPNs 43 . It is supposed that the GH45 genes in the nematode may be horizontally transferred from fungus 44 .…”

Characterization and Functional Importance of Two Glycoside Hydrolase Family 16 Genes from the Rice White Tip Nematode Aphelenchoides besseyi

“…Damage caused by A. besseyi generally reduces rice yields by 12–20% with the annual economic loss estimated at $16 billion [ 3 ]. This nematode has also been found on a wide range of plants, including strawberry, tuberose, [ 4 ] and bird’s-nest fern [ 5 ], exhibiting a robust adaptivity to cope with various hosts.…”

“…A. besseyi tends to multiply on the necrotrophic fungi served as a food source, such as C. lunata [ 9 ] and Botrytis cinerea [ 10 ]. In this scenario, A. besseyi may secrete a myriad of enzymes to degrade fungal cell walls to facilitate its feeding and reproduction [ 5 ].…”