小麦Pm21基因调控的白粉菌早期侵染抑制和寄主细胞反应

携带抗白粉病基因Pm21的小麦材料对白粉病免疫，叶片可见坏死斑。苗期人工接种小麦白粉菌(Blumeria graminis f. sp. tritici)和病原侵染初期的细胞学观察表明，在互作位点，携带Pm21基因的抗病材料上表皮细胞乳突形成时间与感病对照差异不明显，但乳突的大小、致密度、持续时间及乳突中H₂O₂染色较对照有明显差异，并由此显著降低白粉菌的侵入频率。抗病材料上发生多次侵染未成功导致白粉菌附着胞畸形。对于少数成功侵入并形成吸器的白粉菌，抗病材料表皮细胞发生过敏性反应，限制白粉菌吸器和二级菌丝的发展。因此，Pm21调控的白粉病抗病反应在细胞水平上表现为细胞壁加固和过敏性反应的发生。

Primary Infection Suppression of Blumeria graminis f.sp.tritici and Host Cell Responses Regulated by Pm21 Gene in Wheat

Pm21 is a wide-spectrum resistance gene to powdery mildew (Blumeria graminis f. sp. tritici, Bgt) in wheat (Triticum aestivum L.), which originates from Haynaldia villosa. To reveal the mechanism of Pm21-mediated Bgt resistance in wheat at early infection stage, we carried out the cytological observations using wheat line 92R137, carrying Pm21 gene and presenting immunity (but with visible spots on leaves) to Bgt after artificial inoculation with the prevalent Bgt race 15. Chinese Spring (CS) was used as the susceptible control. In wheat–Bgt interaction sites on leaves, papillae formed at a similar time in challenged epidermal cells in both 92R137 and CS. However, the papillae were larger and more compact and persisted in longer time in 92R137 than in CS, resulting in effectively blocking the penetration of Bgt. Accumulation of H₂O₂ was observed in the papillae of 92R137 by DAB staining. Appressorium malformation occurred in 92R137, which was probably caused by the failure of multiple penetration attempts of Bgt. For the small number of Bgt that successfully penetrated the epidermal cells of 92R137, haustorium-dependent hypersensitive reactions were induced to suppress further development of haustoria and secondary hyphae, arresting onset of powdery mildew. Therefore, the major mechanism of Pm21-mediated Bgt resistance involves challenged host cell wall reinforcement and hypersensitive reaction.