Expression of pectinase activity among Aspergillus flavus isolates from southwestern and southeastern United States
2004
Mellon, Jay E. | Cotty, Peter J.
Aspergillus flavus is a widely distributed filamentous fungus that contaminates crops with the potent carcinogen aflatoxin. This species can be divided into S and L strains on the basis of sclerotial morphology. During crop infection, A. flavus can secrete a large array of hydrolytic enzymes.These include pectinase, which aids fungal spread through plant tissues. A survey of pectinase expression by soilisolates derived from different regions of the United States revealed geographic polymorphisms. Strain L isolates from Arizona produced moderate to high levels of a specific pectinase P2c, while S strain isolates produced variable amounts of P2c. In contrast, L strain isolates from southeastern U.S. yielded variable P2c production, while S strain isolates consistently expressed high P2c levels.These results were corroborated by pectinase surveys of additional collections of A. flavus from soil and cottonseed. Expression patterns for P2c and pectinmethylesterase were evaluated for a select number of isolates using an isoelectric focusing technique. Clear zone reactions from the pectinase plate assay corresponded to the presence of P2c, while redring reactions corresponded to the lack of P2c. Commercial cottonseed infected by S strain isolates frequently contained aflatoxin, even when infected by S strain isolates that didnot produce pectinase P2c. Thus, although P2c-lacking isolates have reduced invasiveness, these isolates still have sufficient pathogenicity to cause aflatoxin contamination.
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