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

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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