Apple ring rot, which is caused by Botryosphaeria dothidea, severely affects apple production. The mechanisms employed in apple cells against B. dothidea remain unknown. In this research, the pathogen infection mode and the relationship between cell death and disease resistance in ‘Fuji’/B. dothidea interaction pathosystem were investigated. By using transmission electron microscopy (TEM), our research showed that the pathogen infects apple cells both intracellularly and extracellularly. However, compared with that in immature fruit, the incidence of hyphae in the interior of mature apple fruit cells increased dramatically, suggesting that cell wall-mediated penetration resistance could be important in apple resistance against B. dothidea. TEM ultrastructural characterization identified the nuclear morphology of programmed cell death induction in both apple fruit and callus cells under B. dothidea infection. Overexpression of MdVDAC2 (MDP0000271281), which encodes an outer-membrane localized anion channel protein in mitochondria, significantly promoted cell death under B. dothidea infection and simultaneously inhibited pathogen infection, suggesting that cell death represents a disease resistance mechanism in apple against B. dothidea infection. Furthermore, BdCatalase (KAF4307763), a cytochrome P450 family protein BdCYP52A4 (KAF4300696), and subtilisin-domain containing proteins were identified from B. dothidea-secreted proteins, which suggested the potential involvement of active oxygen species and phytoalexins in combating B. dothidea infection and triggering or dampening apple resistance. Collectively, our research suggested that cell wall-mediated penetration resistance, programmed cell death machinery and microbial effector-interrelated signaling were among strategies recruited in apple to combat B. dothidea. The current research laid the foundation for further investigations into resistance mechanisms in apple.

苹果轮腐病是由Botryosphaeria dothidea 引起的，严重影响苹果生产。苹果细胞中针对B. dothidea的机制仍然未知。在这项研究中，研究了'Fuji'/ B. dothidea相互作用病理系统中的病原体感染模式和细胞死亡与抗病性之间的关系。通过使用透射电子显微镜 (TEM)，我们的研究表明病原体会在细胞内和细胞外感染苹果细胞。然而，与未成熟果实相比，成熟苹果果实细胞内部菌丝的发生率急剧增加，表明细胞壁介导的穿透抗性可能在苹果对 B. dothidea 的抗性中起重要作用. TEM 超微结构表征确定了在B. dothidea感染下苹果果实和愈伤组织细胞中程序性细胞死亡诱导的核形态。在线粒体中编码外膜定位阴离子通道蛋白的MdVDAC2 ( MDP0000271281) 的过表达显着促进了B. dothidea感染下的细胞死亡，同时抑制了病原体感染，表明细胞死亡代表了苹果对B. dothidea的抗病机制感染。此外，BdCatalase (KAF4307763)、一种细胞色素 P450 家族蛋白 BdCYP52A4 (KAF4300696) 和含有枯草杆菌蛋白酶结构域的蛋白质从B. dothidea中鉴定出来-分泌的蛋白质，这表明活性氧和植物抗毒素可能参与对抗B. dothidea感染和触发或抑制苹果抗性。总的来说，我们的研究表明，细胞壁介导的穿透阻力、程序性细胞死亡机制和微生物效应相关信号是苹果招募来对抗B. dothidea 的策略之一。本研究为进一步研究苹果的抗病机制奠定了基础。