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

（1）如我们最近报道的另一种溴病毒春美人潜伏溴病毒（Springbeautylatentbromovirus，SBLV）一样，决明子黄斑溴病毒（Cassiayellowblotchbromovirus，CYBV）被证明能系统而有效地感染模式植物拟南芥。CYBV和SBLV在部分拟南芥品种中表现出不同的侵染力。构建了CYBV基因组RNA的全长cDNA克隆，从中可以转录感染性体外转录物。（2）检测了感染SBLV的拟南芥品种的症状发展。包括S96在内的几个材料对SBLV感染敏感，而包括Col-0在内的其他材料则没有感染或出现轻微症状。遗传研究表明，S96的症状表型受一个半显性基因座控制。我们将该位点命名为SSB 1。Col-0和S96的侵染力在植株和原生质体中基本一致，表明症状表型的差异不是由于SBLV侵染力的不同所致。利用遗传标记将SSB 1定位在第IV染色体上的CAT 2和nga 1107之间。遗传分析表明，SSB 1控制的拟南芥症状发展依赖于水杨酸信号和乙烯信号。（3）雀麦花叶溴病毒（BMV）对拟南芥的侵染能力有限，而SBLV对拟南芥的侵染能力很强。cpr 5的双突变体和三突变体在这些途径被破坏的情况下仍然允许BMV有效地感染拟南芥，这表明cpr 5突变通过独立于赋予SAR的机制来增强BMV增殖。即使在原生质体中，BMV的增殖能力也低于SBLV，但cpr 5突变增强了BMV的增殖能力。

(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.