Matsushita Yosuke, Yanagisawa Hironobu
Institute of Vegetable and Floriculture Science, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, 305-8519, Japan.
Central Region Agricultural Research Centre, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, 305-8666, Japan.
Virus Genes. 2018 Feb;54(1):124-129. doi: 10.1007/s11262-017-1510-7. Epub 2017 Sep 23.
Vertical and horizontal pollen transmission is important for efficient infection by viroids. Vertical pollen transmission of viroids is attributed to the infection by viroid in the embryo sac through infected pollen. To identify the viroid infection in pollen and pollen tubes elongating through the transmitting tract, we used in situ hybridization to histochemically analyze the distribution of Tomato planta macho viroid (TPMVd) in pollen grains, the stigma, and style of petunia plants. TPMVd was present in the generative nucleus and vegetative nucleus of mature infected pollen grains and germinating pollen grains. During pollen tube growth, TPMVd was present in the vegetative nucleus and two sperm nuclei, which were generated by division of the generative nucleus in the style transmitting tract. These findings indicated that viroid infection in sperm nuclei is responsible for vertical pollen transmission of viroids. TPMVd infection from TPMVd-infected pollen tubes to the transmitting tract was not observed. In addition, TPMVd signals were not confirmed in the stigma and transmitting tract of TPMVd-infected petunia plants, suggesting that viroids may not replicate in these tissues at the stage of mature style. Therefore, TPMVd may leak from the pollen tube somewhere in the ovary, except in the transmitting tract, during the horizontal transmission of TPMVd.
垂直和水平花粉传播对于类病毒的有效感染很重要。类病毒的垂直花粉传播归因于受感染花粉通过胚囊感染类病毒。为了鉴定花粉和通过花粉管通道伸长的花粉管中的类病毒感染情况，我们使用原位杂交技术对矮牵牛植株花粉粒、柱头和花柱中番茄雄性化类病毒（TPMVd）的分布进行了组织化学分析。TPMVd存在于成熟受感染花粉粒和萌发花粉粒的生殖核和营养核中。在花粉管生长过程中，TPMVd存在于营养核和两个精核中，这两个精核是由花柱通道中生殖核分裂产生的。这些发现表明精核中的类病毒感染是类病毒垂直花粉传播的原因。未观察到TPMVd从受TPMVd感染的花粉管感染到花柱通道。此外，在受TPMVd感染的矮牵牛植株的柱头和花柱通道中未确认到TPMVd信号，这表明在成熟花柱阶段类病毒可能不在这些组织中复制。因此，在TPMVd水平传播过程中，TPMVd可能在子房的某个部位从花粉管中泄漏出来，花柱通道除外。
