Plant Virus Department, Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures, 38124 Braunschweig, Germany.
Cells. 2021 May 17;10(5):1221. doi: 10.3390/cells10051221.
Cassava brown streak disease (CBSD) is a destructive disease of cassava in Eastern and Central Africa. Because there was no source of resistance in African varieties to provide complete protection against the viruses causing the disease, we searched in South American germplasm and identified cassava lines that did not become infected with the cassava brown streak viruses. These findings motivated further investigations into the mechanism of virus resistance. We used RNAscope in situ hybridization to localize cassava brown streak virus in cassava germplasm lines that were highly resistant (DSC 167, immune) or that restricted virus infections to stems and roots only (DSC 260). We show that the resistance in those lines is not a restriction of long-distance movement but due to preventing virus unloading from the phloem into parenchyma cells for replication, thus restricting the virus to the phloem cells only. When DSC 167 and DSC 260 were compared for virus invasion, only a low CBSV signal was found in phloem tissue of DSC 167, indicating that there is no replication in this host, while the presence of intense hybridization signals in the phloem of DSC 260 provided evidence for virus replication in companion cells. In neither of the two lines studied was there evidence of virus replication outside the phloem tissues. Thus, we conclude that in resistant cassava lines, CBSV is confined to the phloem tissues only, in which virus replication can still take place or is arrested.
木薯褐色条斑病（CBSD）是东非和中非木薯的一种破坏性疾病。由于非洲品种中没有抗源来提供对引起该病的病毒的完全保护，我们在南美种质中进行了搜索，并鉴定出不会感染木薯褐色条斑病毒的木薯品系。这些发现促使我们进一步研究病毒抗性的机制。我们使用 RNAscope 原位杂交技术，对高度抗性（DSC167，免疫）或仅限制病毒感染到茎和根的木薯种质品系（DSC260）中的木薯褐色条斑病毒进行定位。我们表明，这些品系的抗性不是限制长距离运动，而是由于阻止病毒从韧皮部卸载到薄壁细胞中进行复制，从而将病毒限制在韧皮部细胞中。当比较 DSC167 和 DSC260 对病毒入侵时，仅在 DSC167 的韧皮部组织中发现低 CBSV 信号，表明在该宿主中没有复制，而 DSC260 的韧皮部中存在强烈的杂交信号则为病毒在伴胞中的复制提供了证据。在所研究的两个品系中，都没有证据表明病毒在韧皮组织之外复制。因此，我们得出结论，在抗性木薯品系中，CBSD 仅局限于韧皮组织，病毒仍可在其中进行复制或被阻止。
