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

Molecular Characterization of Three B-1,4-Endoglucanase Genes in Pratylenchus loosi and Functional Analysis of Pl-eng-2 Gene

Pratylenchus loosi is an important root-lesion nematode that causes damage to tea plantations in Iran and all over the world. The present study reports on the characterization and evolution of three ß-1,4-endoglucanase genes: Pl-eng-2, Pl-eng-3 and Pl-eng-4. The gene structure of Pl-eng-2 was fully determined with the predicted signal peptide and devoid of the linker domain and carbohydrate-binding domain, while Pl-eng-3 and Pl-eng-4 were only partially sequenced. The transcription of Pl-eng-2 was localized in the secretory esophageal glands of all life stages, but it was upregulated in male and female stages. The exon/intron structures of Pl-eng-2, Pl-eng-3 and Pl-eng-4 confirmed that they resulted from gene duplication followed by sequence and gene structure diversification with loss of the linker domain and carbohydrate-binding domain during evolution. A phylogenetic analysis further confirmed that nematode endoglucanases resulted from the horizontal gene transfer of a bacterial gene, as Pl-eng-3 showed sister relationships with the CelB cellulase of Bacillus subtilis. Silencing Pl-eng-2 by in vitro RNA interference produced a 60% decrease of the transcript level. The reproductive ability of silenced P. loosi showed a 35% reduction of eggs and larval stages compared to untreated nematodes, suggesting that this gene is involved in the early steps of invasion.

Molecular Characterization and Functional Analysis of the Hb-hsp90-1 Gene in Relation to Temperature Changes in Heterorhabditis bacteriophora

Understanding how entomopathogenic nematodes respond to temperature changes and have adapted to the local environment is crucial to improve their potential as biocontrol agents. In order to improve understanding of Heterorhabditis bacteriophora's potential adaptability to future climate changes, full-length cDNA and the corresponding gene of heat shock protein 90 (Hsp90) were isolated and fully characterized. The reproductive potential of the Apulian strain of H. bacteriophora increased when the temperature rose from 23 to 30°C, but no reproduction was found at 12°C. Expression analyses revealed that Hb-hsp90-1 was differentially expressed in Infective Juveniles (IJs) and adults (hermaphrodites, females and males). Up-regulation of Hb-hsp90-1 was higher during the recovery process in Galleria mellonella larvae than adults, thus confirming the protective role of Hb-hsp90-1 in coping with the host environment. Silencing of Hb-hsp90-1 resulted in a significant reduction (76%) in the expression level. Silenced IJs took longer than untreated nematodes to infect G. mellonella, showing that Hb-hsp90-1 could be also involved in chemosensation. Furthermore, the number of adults and IJs recovered from G. mellonella infected with silenced nematodes and incubated at 30°C was higher than that obtained from G. mellonella infected with untreated nematodes. These data confirm the crucial role of Hb-hsp90-1 allowing acclimation to increased temperatures and modulation of the recovery process.