Analysis of a Horizontally Transferred Pathway Involved in Vitamin B6 Biosynthesis from the Soybean Cyst Nematode Heterodera glycines

Abstract

Heterodera glycines is an obligate plant parasite capable of biochemically and developmentally altering its host's cells in order to create a specialized feeding cell. Although the exact mechanism of feeding cell morphogenesis remains a mystery, the nematode's ability to manipulate the plant is thought to be due in part to horizontal gene transfers (HGTs). A bioinformatic screen of the nematode genome has revealed homologues of the genes SNZ and SNO, which comprise a metabolic pathway for the de novo biosynthesis of pyridoxal 5'-phosphate, the active form of vitamin B(6) (VB(6)). Analysis of the 2 genes, HgSNZ and HgSNO, show that they contain nematode-like introns, generate polyadenylated mRNAs, and map to the soybean cyst nematode genetic linkage map, indicating that they are part of the nematode genome. However, gene synteny, protein homology, and phylogenetic evidence suggest prokaryotic origin. This would represent the first case of the HGT of a complete pathway into a nematode or terrestrial animal. VB(6) acts as a cofactor in over 140 different enzymes, and recent studies point toward an important role as a potent quencher of reactive oxygen species. With H. glycines' penchant for acquiring parasitism genes through HGT along with the absence of this pathway in other land-based animals suggests a specific need for VB(6) which may involve the parasite-host interaction.

Ancient gene transfer from algae to animals: Mechanisms and evolutionary significance

“…Moreover, HGT from other free-living organisms has also been reported in cnidarians [39,56,57], bdelloid rotifers [58], insects [59], and nematodes [60-62] and other animals [63]. The acquired genes are often linked to novel phenotypes and abilities in recipient organisms, such as improved preying capability in cnidarians [56] and reduced susceptibility to predation in aphids [59].…”

Horizontal gene transfer in the acquisition of novel traits by metazoans

“…On the other hand, horizontally transferred genes from bacteria encoding proteins participating in the biosynthesis of several types of vitamin B have been described [38,39]. These are probably involved in the processing of plant resources.…”

Analysis of survival and hatching transcriptomes from potato cyst nematodes, Globodera rostochiensis and G. pallida

“…For example, Craig, et al . 38 found vitamin B 6 biosynthesis genes in Heterodera glycines , the soybean cyst nematode. Additional genes involved in vitamin B 1 , B 5 and B 7 biosynthesis with evidence of horizontal gene transfer from bacteria are also found in H .…”