Target search in Aspergillus nidulans for a novel antifungal compound (s) produced by Lysobacter enzymogenes strain C3
Abstract:
Lysobacter enzymogenes strain C3 is an efficient biological control agent in suppressing plant fungal diseases. The production of lytic enzymes is an important mechanism for disease control by C3. It produces antifungal enzymes chitinases and glucanase and also produces other lytic enzymes including protease(s) and lipase(s). Induced resistance is another mechanism for disease control by C3. In attempt to isolate the elicitor for induced resistance we found a heat stable antifungal factor (HSAF). HSAF has broad antifungal spectrum including Candida albicans, Pichia anomala, Bipolaris sorokiniana, Aspergillus nidulans, Fusarium oxysporum f. sp. Phaseoli, Fusarium graminearum, Cryptococcus neoformans, Phytophthora sojae, Pythium ultimum. HSAF treated fungal hyphae shows excessive branching and swelling. To get the clue on its action mode, nucleus division, cell wall deposition, chitin biosynthesis, glucan biosynthesis, ergosterol biosynthesis and cytoskeleton organization were examined. And we found HSAF does not dramatically inhibit nuclear division and the biosynthesis of ergosterol ,chitin and glucan but it alters cell wall deposition pattern and the cytoskeleton organization pattern. To clarify what it the target, we screened plasmid genomic library by complementing the resistant and hypersensitive mutant. One resistant strain UV13 and hypersensitive strain 8-145 were generated and both of them are ts mutants. Complementation analysis showed they mutate at two different genes. Both resistant mutant UV13 and hypersensitive mutant 8-145 were complemented. The complemented plasmid in 8-145 was integrated in genome and can not be recovered. And UV13 contain a mutation at a longevity assurance protein (LAG1) homologous gene which functions as ceramide synthase(a building block for sphingolipid biosynthesis) in Saccharomyces cerevisiae. However, overexpression of LAG1 homolog in wild type strain did not show any elevation on HSAF resistance. And ever-expression of LAG1 in 8-145 partially elevates its heat tolerance but did not change HSAF sensitivity. Before we identify the mutated gene in 8-145, no conclusion can be made.
Shaojie Li
Graduate student in plant pathology
406 Plant Sciences Hall
Lincoln, NE68583