Deletion of the benzoxazinoid detoxification gene NAT1 in Fusarium graminearum reduces deoxynivalenol in spring wheat

Benzoxazinoid (Bx) metabolites produced by wheat and other members of the Poaceae have activity against Fusarium sp. that cause cereal diseases including Fusarium head blight (FHB) on wheat and barley. Certain Bx metabolites can be detoxified by Fusarium sp. with the arylamine N-acetyltransferase NAT1. Investigation of this pathway may reveal strategies for increasing FHB resistance, such as selection for higher levels of Bx metabolites within existing germplasm and/or engineering fungal susceptibility via host induced silencing of NAT1. We assessed the reactions of fifteen wheat cultivars or breeding lines adapted to the Northwestern United States to infection with F. graminearum Δnat1 mutants that should be sensitive to Bx metabolites. Significant differences were noted in disease severity and deoxynivalenol (DON) among the cultivars 21 d after inoculation with either mutant or wildtype (PH1) strains. Mutant vs. wildtype strains did not result in significant variation for infection severity (as measured by % infected florets), but inoculation with Δnat1 mutants vs. wildtype resulted in significantly lower DON concentrations in mature kernels (p Δnat1 mutants (severity = 61%, DON = 30 ppm). The cultivar most susceptible to infection was Kelse with PH1 (severity = 100%, DON = 292 ppm) and Δnat1 mutants (severity = 100%, DON = 158 ppm). We hypothesized that sub-lethal Bx metabolite levels may suppress DON production in F. graminearum Δnat1 mutants. In vitro assays of Bx metabolites BOA, MBOA, and DIMBOA at 30 μM did not affect growth, but did reduce DON production by Δnat1 and PH1. Although the levels of Bx metabolites are likely too low in the wheat cultivars we tested to suppress FHB, higher levels of Bx metabolites may contribute towards reductions in DON and FHB.

小麦及其他禾本科（Poaceae）植物产生的苯并恶嗪类（Benzoxazinoid，Bx）代谢物，对引发包括小麦和大麦赤霉病（Fusarium head blight，FHB）在内的谷类病害的镰孢菌属（Fusarium sp.）具有抑菌活性。部分Bx代谢物可被镰孢菌属通过芳胺N-乙酰转移酶NAT1（arylamine N-acetyltransferase NAT1）进行解毒。对该代谢通路的研究或可揭示提升赤霉病抗性的策略，例如在现有种质资源中筛选高Bx代谢物含量的品种，以及通过寄主诱导的NAT1基因沉默使真菌丧失解毒能力。

我们针对美国西北部适配的15个小麦品种或育种品系，评估其接种禾谷镰孢菌（Fusarium graminearum，F. graminearum）Δnat1突变体后的抗病反应——该突变体对Bx代谢物敏感。接种突变体或野生型（PH1）菌株21天后，各品种的病害严重度与脱氧雪腐镰刀菌烯醇（deoxynivalenol，DON）含量均存在显著差异。突变体与野生型菌株在侵染严重度（以受侵染小穗百分比计）上未产生显著差异，但与野生型菌株接种相比，Δnat1突变体接种后的成熟籽粒中DON浓度显著更低（p < 0.05；Δnat1突变体组：病害严重度为61%，DON含量为30 ppm）。感染性最强的小麦品种为Kelse，接种PH1野生型时病害严重度达100%，DON含量为292 ppm；接种Δnat1突变体时病害严重度仍为100%，DON含量为158 ppm。

我们提出假说：亚致死浓度的Bx代谢物可能会抑制禾谷镰孢菌Δnat1突变体的DON合成。体外实验显示，30 μM浓度的Bx代谢物BOA、MBOA与DIMBOA不会影响真菌生长，但可降低Δnat1突变体与PH1野生型的DON产量。尽管本次测试的小麦品种中Bx代谢物含量可能过低，无法有效抑制赤霉病，但更高水平的Bx代谢物或可降低DON积累与赤霉病病害严重程度。