Molecular Characterization of Arginine Kinases in the Soybean Cyst Nematode (Heterodera glycines)

Arginine kinase (AK) is a phosphagen kinase that plays a key role in energy mobilization in invertebrates. Alignment of expressed sequence tags (ESTs) for soybean cyst nematode (SCN) (Heterodera glycines) produced two separate contiguous sequences (contigs) and three singletons encoding peptides with high similarity to AKs. One contig, Hg-AK1, had 244 ESTs in the alignment whereas the other, Hg-AK2, had only three; nonetheless, the consensus sequence for Hg-AK1 was missing much of the 5' end. Polymerase chain reaction (PCR) was used to prepare clones that were then sequenced to obtain full-length sequences for both Hg-AK1 and Hg-AK2. Hg-AK1 has an open reading frame of 1080 nucleotides (nt) encoding a protein of 360 amino acids (aa) with a predicted molecular weight of 40 kDa. The open reading frame for Hg-AK2 is 1221 nt, 407 aa, and 46 kDa with a 71% aa identity with Hg-AK1. Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) indicated that Hg-AK1 and Hg-AK2 are expressed constitutively throughout the SCN life cycle. Phylogenetic analysis of peptide sequences for near full-length nematode contigs and other AKs in the Swisspro database indicates that the nematode AKs evolved from a single gene after divergence of insects and nematodes.