State Key Laboratory of Crop Biology, College of Horticulture Science and Engineering, Shandong Agricultural University, Tai'an, China.
Mol Plant Pathol. 2022 Mar;23(3):383-399. doi: 10.1111/mpp.13166. Epub 2021 Nov 26.
Apple necrotic mosaic virus (ApNMV) is highly associated with the occurrence of apple mosaic disease in China. However, ApNMV-host interactions and defence mechanisms of host plants against this virus are poorly studied. Here, we report that nitrate treatment restrains ApNMV genomic RNA accumulation by destabilizing viral replication protein 1a through the MdBT2-mediated ubiquitin-proteasome pathway. MdBT2, a nitrate-responsive BTB/TAZ domain-containing protein, was identified in a yeast two-hybrid screen of an apple cDNA library using viral protein 1a as bait, and 1a was further confirmed to interact with MdBT2 both in vivo and in vitro. It was further verified that MdBT2 promoted the ubiquitination and degradation of viral protein 1a through the ubiquitin-proteasome pathway in an MdCUL3A-independent manner. Viral genomic RNA accumulation was reduced in MdBT2-overexpressing transgenic apple leaves but enhanced in MdBT2-antisense leaves compared to the wild type. Moreover, MdBT2 was found to interfere with the interaction between viral replication proteins 1a and 2a by competitively interacting with 1a. Taken together, our results demonstrate that nitrate-inducible MdBT2 functions as a limiting factor in ApNMV viral RNA accumulation by promoting the ubiquitination and degradation of viral protein 1a and interfering with interactions between viral replication proteins.
苹果坏死花叶病毒（ApNMV）与中国苹果花叶病的发生高度相关。然而，ApNMV 与宿主的相互作用以及宿主植物对该病毒的防御机制研究甚少。在这里，我们报告硝酸盐处理通过 MdBT2 介导的泛素-蛋白酶体途径破坏病毒复制蛋白 1a 来抑制 ApNMV 基因组 RNA 的积累。MdBT2 是一种硝酸盐响应的 BTB/TAZ 结构域蛋白，在以病毒蛋白 1a 为诱饵的苹果 cDNA 文库酵母双杂交筛选中被鉴定出来，并且 1a 进一步被证实与 MdBT2 在体内和体外相互作用。进一步证实，MdBT2 通过泛素-蛋白酶体途径在不依赖 MdCUL3A 的情况下促进病毒蛋白 1a 的泛素化和降解。与野生型相比，MdBT2 过表达转基因苹果叶片中的病毒基因组 RNA 积累减少，而 MdBT2 反义叶片中的病毒基因组 RNA 积累增加。此外，发现 MdBT2 通过与 1a 竞争相互作用来干扰病毒复制蛋白 1a 和 2a 之间的相互作用。总之，我们的结果表明，硝酸盐诱导的 MdBT2 通过促进病毒蛋白 1a 的泛素化和降解以及干扰病毒复制蛋白之间的相互作用，作为 ApNMV 病毒 RNA 积累的限制因素发挥作用。
