Liu L, Saunders K, Thomas C L, Davies J W, Stanley J
Department of Virus Research, John Innes Centre, Norwich Research Park, Colney, NR4 7UH, United Kingdom.
Virology. 1999 Apr 10;256(2):270-9. doi: 10.1006/viro.1999.9616.
It has previously been reported that complementary-sense gene products of wheat dwarf virus (WDV), a geminivirus of the genus Mastrevirus that infects monocotyledonous plants, bind to human and maize retinoblastoma (Rb) protein. Rb proteins control cell-cycle progression by sequestering transcription factors required for entry into S-phase, suggesting that the virus modifies the cellular environment to produce conditions suitable for viral DNA replication. Using a yeast two-hybrid assay, we have investigated whether the complementary-sense gene products of bean yellow dwarf virus, a mastrevirus that is adapted to dicotyledonous plants, also bind maize Rb protein. We demonstrate that whereas RepA binds to Rb protein, Rep does not, suggesting that RepA alone regulates host gene expression and progression of cells to S-phase. RepA mutants containing L --> I, C --> S, C --> G, and E --> Q mutations within the consensus Rb protein binding motif LXCXE retained the ability to bind to Rb, but with reduced efficiency. Most notably, the E --> Q mutation reduced binding by approximately 95%. Nonetheless, all LXCXE mutants were able to replicate in tobacco protoplasts and to systemically infect Nicotiana benthamiana and bean, in which they produced wild-type symptoms.
先前有报道称，小麦矮缩病毒（WDV）是一种感染单子叶植物的 Mastrevirus 属双生病毒，其互补链基因产物可与人和玉米的视网膜母细胞瘤（Rb）蛋白结合。Rb 蛋白通过隔离进入 S 期所需的转录因子来控制细胞周期进程，这表明该病毒会改变细胞环境以创造适合病毒 DNA 复制的条件。利用酵母双杂交试验，我们研究了适应双子叶植物的 Mastrevirus 属病毒——菜豆黄矮病毒的互补链基因产物是否也能结合玉米 Rb 蛋白。我们证明，虽然 RepA 能与 Rb 蛋白结合，但 Rep 不能，这表明仅 RepA 可调节宿主基因表达以及细胞进入 S 期的进程。在共有 Rb 蛋白结合基序 LXCXE 内含有 L→I、C→S、C→G 和 E→Q 突变的 RepA 突变体仍保留与 Rb 结合的能力，但效率降低。最显著的是，E→Q 突变使结合能力降低了约 95%。尽管如此，所有 LXCXE 突变体都能够在烟草原生质体中复制，并系统性感染本氏烟草和菜豆，在这些植物中产生野生型症状。
