Molecular cloning and functional analysis of Arabidopsis thaliana genes involved in bromovirus multiplication

(1)决明黄斑雀斑病毒（CYBV）被证明可以系统有效地感染模式植物物种拟南芥，正如我们最近报道的另一种雀斑病毒，春美潜伏雀斑病毒（SBLV）。 CYBV和SBLV在拟南芥的一些种质中表现出不同的感染性。构建了 CYBV 基因组 RNA 的全长 cDNA 克隆，可以从中转录感染性的体外转录物。 (2)检测感染SBLV的拟南芥种质的症状发展情况。包括S96在内的几种材料对SBLV感染敏感，而包括Col-0在内的其他材料则无症状或出现轻微症状。遗传学研究表明，S96 的症状表型由单个半显性基因座控制。我们已指定该位点 SSB1。 Col-0和S96之间SBLV在植物和原生质体中的感染力相当，表明症状表型的变化并不是由于SBLV的感染力不同所致。通过使用遗传标记，SSB1被定位在IV号染色体上的CAT2和nga1107之间。遗传分析表明，拟南芥中受SSB1控制的症状发展依赖于水杨酸信号传导和乙烯信号传导。 (3)溴花叶病毒(BMV)对拟南芥的感染有限，而SBLV则能有效地感染拟南芥。在筛选具有改变的防御反应的拟南芥突变体时，发现 BMV 通过 cpr5 突变系统且有效地感染拟南芥，已知 cpr5 突变可组成性表达系统获得性抗性 (SAR)。这些途径被破坏的 cpr5 双突变体和三突变体仍然允许 BMV 有效感染拟南芥，这表明 cpr5 突变通过独立于赋予 SAR 的机制增强 BMV 增殖。即使在原生质体中，BMV 的增殖能力也低于 SBLV，并且通过 cpr5 突变而增强。

(1)Cassia yellow blotch bromovirus(CYBV) was shown to infect systemically and efficiently a model plant species, Arabidopsis thaliana, as we recently reported for another bromovirus, Spring beauty latent bromovirus(SBLV). CYBV and SBLV showed different infectivities in some accessions of A.thaliana. Full-length cDNA clones of CYBV genomic RNAs were constructed, from which infectious in vitro transcripts can be transcribed. (2)Symptom development was examined in A.thaliana accessions infected with SBLV. Several accessions including S96 were sensitive to SBLV infection, while the other accessions including Col-0 were symptomless or developed mild symptoms. Genetic study suggested that the symptom phenotype of S96 is controlled by a single semidominant locus. We have designated this locus SSB1. Infectivity of SBLV in plants and protoplasts were comparable between Col-0 and S96, indicating that variation of symptom phenotype was not due to the different infectivity of SBLV. By using genetic markers, SSB1 was mapped between CAT2 and nga1107 on chromosome IV. Genetic analyses suggest that symptom development in A.thaliana controlled by SSB1 is dependent on salicylic acid signaling and ethylene signaling. (3)Brome mosaic bromovirus(BMV) shows limited infection in A.thaliana, while SBLV efficiently infects it. In a screening of Arabidopsis mutants with altered defense responses, BMV was found to infect A.thaliana systemically and efficiently by the cpr5 mutations, which have been known to constitutively express systemic acquired resistance(SAR). Double and triple mutants of cpr5 with these pathways disrupted still allowed BMV to infect A.thaliana efficiently, suggesting that cpr5 mutations enhance BMV multiplication by the mechanism independent of that to confer SAR. Even in protoplasts, multiplication ability of BMV was lower than that of SBLV and was enhanced by the cpr5 mutations.