Specificity of Plant Infection : Molecular Mechanism of Determination of Basic Compatibility by Host-Specific Toxins

已知某些真菌病原体产生宿主特异性毒素(HST)，作为植物感染基本亲和性的决定因素。目前产生HST的病原菌约有20种。我们发现，油菜链格孢菌(Alternaria Brassicicola)、黄瓜致病类型黄瓜(Corynespora Cassiicola)和番茄致病类型黄瓜棒孢霉(Corynespora Cassiicola)以及球孢霉(Stemphlium Vesicarium)分别产生新的HST，命名为AB-、CCC-、CCT-和SV-毒素。与其他低分子次生代谢产物不同，AB-毒素是一种蛋白质，大小约为35kDa。甘蓝型油菜仅在寄主叶片上从萌发的孢子中释放AB-毒素，表明该病原菌AB-毒素的产生是由寄主相关因子诱导的。链格孢霉病原菌有7种致病型。利用REMI方法将番茄HST(AL-毒素)缺失突变体转化为致病型。另一方面，利用由环肽合成酶基因设计的引物，从苹果致病类型中获得了聚合酶链式反应产物。这些突变体的详细分子分析和聚合酶链式反应产物的…还有更多的项目正在进行中。用聚合酶链式反应(PFGE)对互隔交链孢霉致病类型进行了核型分析。在所有致病类型中，普遍检测到一条1.6Mb的小条带。利用苹果致病类型的聚合酶链式反应产物进行Southern分析表明，AM-毒素合成基因存在于小染色体上。日本梨和苹果致病类型互隔交链孢霉产生的HSTs(AK-毒素和AM-毒素)分别对感病品种的质膜(Pm)和叶绿体(Cs)起主要作用。因此，从各自的寄主中分离Pms和Cs，并利用生物传感器分析Pms或Cs中HSTs与蛋白质之间的相互作用。结果表明，感病品种的Pms和Cs中分别存在AK和AM毒素结合蛋白(受体)。采用双向凝胶电泳法对苹果叶片总蛋白进行了分析。仅在感病品种中检测到60 kDa蛋白，等电点为5.5。对这些蛋白质的分离和鉴定正在进行中。较少

Certain fungal pathogens are known to produce host-specific toxins (HSTs) as determinants of basic compatibility in plant infection. There are now about twenty pathogens that produce HST.We found that Alternaria brassicicola, cucumber pathotype and tomoto pathotype of Corynespora cassiicola, and Stemphylium vesicarium produce new HSTs named AB-, CCC-, CCT-and SV-toxins, respectively. Unlike other HSTs which are low-molecular-weight secondary metabolites, AB-toxin was a protein and estimated to be 35 kDa.A.brassicicola released AB-toxin from the germinating spores only on host leaves, indicating that AB-toxin production by the pathogen is induced by host-related factors. There are seven pathotypes in A.alternata pathogens. HST (AL-toxin) deficient mutants from tomato to pathotype using REMI method. On the other hand, PCR products were obtained from apple pathotypes, using primers designed from cyclic peptide synthase genes. Detailed molecular analysis of these mutants and PCR products a … More re now in progress. Electrophoreic karyotyping of A.alternata pathotypes were determined by PFGE.In all pathotypes, a chromosomal band with small size of <1.6 Mb was detected commonly. Southern analysis using PCR products from apple pathotype showed that AM-toxin synthesis gene exists in the small chromosome.HSTs (AK-toxin and AM-toxin) produced by Japanese pear and apple pathotypes of A.alternata have primary effects on plasma membranes (PMs) and chloroplasts (Cs) of susceptible cultivars, respectively. Therefore, PMs and Cs were isolated from respective hosts, and interaction between HSTs and proteins in PMs or Cs was analyzed by using a biosensor. Results suggest that AK- and AM-toxin-binding proteins (receptors) exist in PMs and Cs of susceptible cultivars, respectively. Total proteins of apple leaves were analyzed by 2-D gel electrophoresis. A spot of 60 kDa protein with pI of 5.5 was detected only in susceptible cultivars. Isolation and characterization of these proteins is in progress. Less