Characterization of Alternaria alternata glucanase genes expressed during infection of resistant and susceptible persimmon fruits

Abstract

Preharvest treatment with gibberellic acid (GA3) or its inhibitor paclobutrazol (PBZ) can reduce or increase, respectively, the susceptibility of persimmon fruits to Alternaria alternata. This was suggested to be the result of the ability of the fungus and produced endoglucanases to induce symptom development. To evaluate the importance of glucanases during A. alternata attack, five glucanase genes, corresponding to the C, F, and K families, were cloned from A. alternata using 'family-specific' oligonucleotide primers. The genes, present in a single copy, encode for exoglucanases AaC1 and AaC2, endoxylanase AaF1, endoglucanase AaK1, and the mixed-linked glucanase AaMLG1. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis of RNA extracted from persimmon fruits, 2 and 4 days post-infection with A, alternata, showed the expression of all five glucanase genes in GA3- and PBZ-treated fruits. However, transcription levels and enzyme production of the endoglucanase (AaK1) and one exoglucanase (AaC1) were enhanced during A. alternata growth on cell walls from susceptible PBZ-treated fruits, whereas the expression of these genes and their enzyme production were significantly reduced in resistant GA3-treated fruits. The present results suggest the involvement of endo- and exoglucanase in symptom development caused by A. alternata in resistant and susceptible persimmon fruits.