Cell wall remodeling in woody tung oil tree root xylem contributes to deterrence of the Fusarium wilt pathogen

Tung oil tree (Vernicia fordii), is renowned for production of unique tung oil, which has been suffered Fusarium wilt disease. Intriguingly, its sister species, woody tung oil trees (V. montana) exhibit high resistance to Fusarium. oxysporum f. sp. fordii (Fof-1) infection. We hypothesize that the xylem cells of V. montana roots might act as physical barriers to deter invasion of the soil-borne Fusarium pathogen. To test this, we investigated the potentially different phenotypic and physiological behaviors of the root xylem cells between V. montana and V. fordii responding to Fof-1. The result showed that pathogen could invade the root xylem of V. fordii but failed to enter the root xylem of V. montana. After Fof-1 infection, the cell wall thickness in V. montana root xylem was statistically increased. A statistically significant increase of lignin in the early stage, and the ratio of S:H lignin and hemicellulose content in the later infection stage were viewed in the V. montana root xylem cell wall. Further comparative metabolomic analysis showed that some intermediary metabolites in the lignin pathways, including cinnamic acid, scopoletin and coumarin, were enriched in V. montana root xylem cells after Fof-1 infection. Consistent with this, in V. montana, KEGG enrichment result also support the evidence that the upregulated genes were enriched in this pathway. The hub genes of lignin biosynthesis pathway in V. montana were further selected and verified using qRT-PCR. Together, our data demonstrated that the remodeling of cell wall in V. montana root xylem make primary contributions to decrease the Fof-1 infection. Promisingly, the discovery offers an opportunity to explore an effective strategy for breeding Fusarium resistant tung oil trees.