The role of heterodera glycines biotin synthase in the nematode-soybean interactions
Heterodera glycines, the soybean cyst nematode (SCN), is a plant-parasitic nematode capable of manipulating host plant biochemistry and development. Many studies have shown 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 avirulent and virulent HgBioB alleles, a complementation experiment using mutant Escherichia coli with these two HgBioB alleles was conducted. Here we report that avirulent nematodes produce an active biotin synthase while virulent ones contain an inactive form of the enzyme. Moreover, we conclude from the sequencing analysis of SCN field populations that in nature the HgBioB gene contains a diverse mixture consisting of both avirulent and virulent alleles, but the virulent forms are more prevalent. We hypothesize that a lack of HgBioB activity within the virulent SCN could allow the nematode to evade a dethiobiotin-related toxin defense mechanism in host plants. Specifically, we showed that all soybean cultivars accumulate detectable levels of α-methyldethiobiotin (α-MDB), a dethiobiotin-related toxin found in bacteria. This is the first report of detecting α-MDB from soybean or any plant. Future work will determine if there is a significant difference in α-MDB levels between resistant and susceptible soybean cultivars.
Heterodera glycines, biotin, vitamin B7, biotin synthase, dethiobiotin, α-methyldethiobiotin, α-methylbiotin, horizontal gene transfer, sequence polymorphisms
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign