State Key Laboratory of Crop Biology, Shandong Key Laboratory of Crop Biology, College of Agronomy, Shandong Agricultural University, Tai'an, 271018, PR China.
State Key Laboratory of Crop Biology, Shandong Key Laboratory of Crop Biology, College of Agronomy, Shandong Agricultural University, Tai'an, 271018, PR China.
Plant Sci. 2018 Jul;272:255-266. doi: 10.1016/j.plantsci.2018.04.015. Epub 2018 Apr 20.
The resistance to Fusarium head blight (FHB) in wheat is mainly via the restrain of fungal expansion through spike rachis (type II resistance). In order to unravel the resistance mechanisms, Brachypodium distachyon 21 (Bd21), a monocotyledonous model plant, was previously proved to interact with F. graminearum, while the disease development in spike still needs to be explored in detail. Herein, it is found that the fungal spores mainly germinate on pistil of Bd21, then the hyphae rapidly extend to the bottom of floret and enter spike rachis, similar with the infection progress in wheat. However, structural difference of spike rachis was found between Brachypodium and wheat. It was found that the spread of the fungus through the rachis node of inoculated spikelets is an important index for the evaluation of type II FHB resistance in Brachypodium under optimal conditions at 28 °C and 50%-70% humidity. To verify the feasibility of this strategy, the transcription factor TaTGA2 was overexpressed in Bd21, and transgenic plants were found to show improved resistance to F. graminearum in both spikes and detached leaves, which was further supported by the increased disease severity when silencing TaTGA2 in the wheat cultivar "Sumai 3" or in tilling "Kronos" mutants. Except for Bd21, another 49 Brachypodium germplasms were further screened for FHB resistance, and three moderately susceptible germplasms, namely, PI 317418, W6-39284, and PI 254868, feasible for transformation, were determined to be better hosts than Bd21 when evaluating heterologous genes that positively regulate FHB resistance. The present study also observed variations in the levels of FHB resistance between coleoptiles and spikes or transgenic plants and natural germplasms.
小麦对镰刀菌穗腐病（FHB）的抗性主要通过穗轴（II 型抗性）抑制真菌扩展来实现。为了揭示其抗性机制，先前已证明单子叶模式植物短柄草 21 号（Bd21）与禾谷镰刀菌互作，然而，穗部的病害发展仍需详细研究。本文发现，真菌孢子主要在 Bd21 的雌蕊上萌发，然后菌丝迅速延伸到底部小花，并进入穗轴，与小麦的感染进程相似。然而，在 Brachypodium 和小麦之间发现了穗轴的结构差异。在 28°C 和 50%-70%湿度的最佳条件下，通过接种小穗的穗轴节间传播真菌是评估 Brachypodium 中 II 型 FHB 抗性的重要指标。为了验证这一策略的可行性，将转录因子 TaTGA2 在 Bd21 中过表达，发现转基因植株在穗部和离体叶片中对禾谷镰刀菌的抗性增强，当在小麦品种“Sumai 3”或突变体“Kronos”中沉默 TaTGA2 时，病害严重程度进一步增加，这进一步支持了这一结论。除了 Bd21 之外，还进一步筛选了 49 份短柄草种质资源以评估其对 FHB 的抗性，发现三个中度敏感的种质资源，即 PI 317418、W6-39284 和 PI 254868，在转化评估正向调控 FHB 抗性的异源基因时，它们比 Bd21 更适合作为宿主。本研究还观察到 coleoptiles 和 spikes 或转基因植株与自然种质资源之间 FHB 抗性水平的变化。
