MOLECULAR BASIS FOR SPECIALIZATION AND EVOLUTION OF PATHOGENICITY IN ALTERNARIA PATHOGENS THAT HOST-SPECIFIC TOXINS INVOLVE IN

从柑桔褐斑病菌澳大利亚菌株中分离到一种新的寄主特异性毒素（HST），测定其结构，命名为ACT-toxin IIIb。建立了一种快速灵敏的al毒素测定方法。研究了HSTs在真菌病原体识别宿主过程中与植物防御反应相关的关键作用。在限制性内切酶的作用下，利用携带hph、gpd和trpC基因的pAN7-1质粒异位整合转化了不同病型交替稻的原生质体，克隆了参与HST生物合成的基因。几个转化子被发现缺乏产生HSTs的能力，并且发现它们随机地在单个位点上整合了一个pAN7-1拷贝。通过从缺乏HST的转化子中修复具有侧链基因组序列的整合质粒DNA，可以分离出含有HST合成基因的DNA片段。电泳核型分析表明，该植物有8 ~ 9条染色体，染色体长度在0.6 ~ 5.5 Mb之间，基因组总长度在22 ~ 24mb之间。b染色体可能与每种病型的特定致病性相关。有些植物在细胞融合中存在不亲和性。

A new host-specific toxin (HST) was isolated from Australian strains of brown spot pathogen of tangerine, determined the structure, and named ACT-toxin IIIb. A rapid and sensitive procedure of AL-toxin determination was established. A key role of HSTs in host recognition by fungal pathogens was investigated in relation to plant defense reactins. For cloning gene (s) involved in biosynthesis of such HST,protoplasts of different pathotypes of Alternaria alternata were transformed utilizing ectopic integration of pAN7-1 plasmid carrying hph, gpd, and trpC genes in the presence of restriction enzymes. Several transformants were found lacked the ability to produce HSTs, and found they randomly have a single copy of pAN7-1 integrated at single site. Isolation of DNA fragments containing HST synthesis gene (s) by rescuing the integrated plasmid DNA with a flanking genomic sequence from HST-deficient transformants may possible. Electrophoretic karyotyping suggested that A.alternata has 8 to 9 chromosomes ranging from 0.6 Mb to 5.5 Mb, and its total genomesize probably is 22-24Mb. B-chromosomes might be correlated to specific pathogenicity of each pathotype. Some A.alternata have incompatibility in cell fusion.