Desiccation stress of entomopathogenic nematodes induces the accumulation of a novel heat-stable protein

The present study describes a novel heat-stable, water-stress-related protein with a molecular mass of 47 kDa (designated Desc47) in the entomopathogenic nematode Steinernema feltiae (IS-6). The protein was accumulated about 10-fold (from 7.84 +/- 1.85 to 74.09 +/- 43.5 % relative content level [RCL]) in dehydrated clumps of infective juveniles (IJs), which had lost 344 % of their initial water content (from 65.1 +/- 17.9 % to 42.7 +/- 0.72 %) in a desiccation-tolerance-inducing treatment (97 % relative humidity [RH] for 3 days). The appearance of Desc47 was accompanied by trehalose accumulation (from 300 to 600 mg trehalose/g protein) during the process of inducing the IJs into a quiescent anhpdrobiotic state. A second cycle of IJ dehydration did not alter the RCL of Desc47 (79 3 % for the first cycle and 73.3 %, for the second cycle). Desc47 retained its high RCL (69.7 %) in rehydrated active IJs for 3 days, reaching 51.2% of its initial RCL only after a week. No homology to other known proteins was found by mass-spectrometry electrospray-ion-trap analysis. However, of the 5 sequences obtained from the protein (ranging from 11 to 21 amino acids), the 21-amino-acid peptide N V A S D A V E T V G N A A G Q A G (D/T) A V showed excellent homology (74 % identity in 19 amino acids) to the cold-responsive protein COR14b (g6564861) from Triticum aestivum. In the Caenorhabditis elegans predicted proteome database search, the N21 yielded the first-best identity score (59 %;, identity in 17 amino acids) to the CE-LEA homologue protein (g2353333). In plants, COR and LEA are related proteins, heat-stable, which are expressed in response to both dehydration and cold acclimation. The implication of the involvement of Desc47 and the osmoprotectant trehalose in the desiccation-tolerance mechanisms of S. feltiae is discussed.