Abstract
Heterodera glycines, the soybean cyst nematode (SCN), is a plant-parasitic nematode capable of manipulating host plant biochemistry and development. Many studies have suggested that the nematode has acquired genes from bacteria via horizontal gene transfer events (HGTs) that have the potential to enhance nematode parasitism. A recent allelic imbalance analysis identified two candidate virulence genes, which also appear to have entered the SCN genome through HGTs. One of the candidate genes, H. glycines biotin synthase (HgBioB), contained sequence polymorphisms between avirulent and virulent inbred SCN strains. To test the function of these HgBioB alleles, a complementation experiment using biotin synthase-deficient Escherichia coli was conducted. Here, we report that avirulent nematodes produce an active biotin synthase while virulent ones contain an inactive form of the enzyme. Moreover, sequencing analysis of HgBioB genes from SCN field populations indicates the presence of diverse mixture of HgBioB alleles with the virulent form being the most prevalent. We hypothesize that the mutations in the inactive HgBioB allele within the virulent SCN could result in a change in protein function that in some unknown way bolster its parasitic lifestyle.
Highlights
What makes matters worse is the nematode’s ability to persist in soils for 10 or more years even in the absence of a soybean host (Riggs, 2004)
The SPRYSEC effector protein Gp-RBP-1 secreted from an esophageal gland in G. pallida (Sacco et al, 2009), the venom allergen-like effector protein Gr-VAP1 secreted from an esophageal gland in G. rostochiensis (LozanoTorres et al, 2012), MAP-1 secreted from amphids in Meloidogyne incognita (Semblat et al, 2001), and a SNARE-like protein (HgSLP-1) secreted from an esophageal gland in H. glycines (Bekal et al, 2015) appear to act as avirulence genes
We compared the enzymatic activities of biotin synthase genes from virulent and avirulent inbred soybean cyst nematode (SCN) strains and showed that the HgBioB-vir from virulent nematodes lacked activity while the HgBioB-avr from avirulent nematodes was fully active, suggesting HgBioB is important in SCN virulence
Summary
What makes matters worse is the nematode’s ability to persist in soils for 10 or more years even in the absence of a soybean host (Riggs, 2004). Some of the secreted proteins are closely related to bacterial proteins, suggesting that they have been acquired from bacteria through horizontal gene transfer events (HGTs) (Smant et al, 1998; Lambert et al, 1999; Davis et al, 2000; Bird et al, 2003; Bekal et al, 2015) While these studies focusing on secreted proteins and HGT candidates have been productive for understanding the molecular basis of nematode-host interactions, non-secreted proteins, enzymes, and metabolites have been overlooked; horizontally transferred genes coding for nonsecreted proteins/enzymes with bacterial homology could play a critical role in SCN biology, parasitism, and (a)virulence. To support or refute this hypothesis, we tested the function of the two HgBioB alleles to ascertain if any functional differences could be detected between the virulent and avirulent forms of the enzyme
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