An arabinose-induced enhancement of asexual reproduction and concomitant changes in metabolic state in the filamentous fungus Bipolaris maydis.

l-Arabinose, a major constituent pentose of plant cell-wall polysaccharides, has been suggested to be a less preferred carbon source for fungi but to be a potential signalling molecule that can cause distinct genome-wide transcriptional changes in fungal cells. Here, we explore the possibility that this unique pentose influences the morphological characteristics of the phytopathogenic fungus Bipolaris maydis strain HITO7711. When grown on plate media under different sugar conditions, the mycelial dry weight of cultures on l-arabinose was as low as that with no sugar, suggesting that l-arabinose does not substantially contribute to vegetative growth. However, the intensity of conidiation on l-arabinose was comparable to or even higher than that on d-glucose and on d-xylose, in contrast to the poor conidiation under the no-sugar condition. To explore the physiological basis of the passive growth and active conidiation on l-arabinose, we next investigated cellular responses of the fungus to these sugar conditions. Transcriptional analysis of genes related to carbohydrate metabolism showed that l-arabinose stimulates carbohydrate utilization through the hexose monophosphate shunt (HMP shunt), a catabolic pathway parallel to glycolysis and which participates in the generation of the reducing agent NADPH (the reduced form of nicotinamide adenine dinucleotide phosphate). Then, the HMP shunt was impaired by disrupting the related gene BmZwf1, which encodes glucose-6-phosphate dehydrogenase in this fungus. The resulting mutants on l-arabinose showed remarkably decreased conidiation, but a conversely increased mycelial dry weight compared with the wild-type. Our study demonstrates that l-arabinose acts to enhance resource allocation to asexual reproduction in B. maydis HITO7711 at the cost of vegetative growth, and suggests that this is mediated by the concomitant stimulation of the HMP shunt.

Synthesis and Investigation of Tetrahydro-ß-carboline Derivatives as Inhibitors of Plant Pathogenic Fungi.

A series of tetrahydro-ß-carbolines substituted with an alkyl or acyl side chain was synthesized and screened for its antifungal activity against plant pathogenic fungi (Bipolaris oryzae, Curvularia lunata, Fusarium semitectum, and Fusarium fujikuroi). The structure activity relationship revealed that the substituent at the piperidine nitrogen plays an important role for increasing antifungal activities. In this series, 2-octyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole (3g) displayed potent antifungal activities with a minimum inhibitory concentration of 0.1 µg/mL, including good inhibitory activity to the radial growth of fungus at a concentration of 100 µg/mL compared to amphotericin B.

Antifungal and Antimicroalgal Trichothecene Sesquiterpenes from the Marine Algicolous Fungus Trichoderma brevicompactum A-DL-9-2.

Eight new trichothecene derivatives, trichodermarins G-N (1-8), and two new cuparene derivatives, trichocuparins A (9) and B (10), as well as six known trichothecenes (11-16) were isolated from the fungal strain Trichoderma brevicompactum A-DL-9-2 obtained from the inner tissue of the marine red alga Chondria tenuissima. The structures and relative configurations of 1-10 were assigned by NMR and MS data, and the absolute configurations of 1, 2, and 9 were established by X-ray diffraction. Compound 8 features an aminosugar unit bond to the trichothecene framework for the first time, while 9 and 10 represent the first occurrence of cuparene sesquiterpenes in Trichoderma. All the isolates were assayed for growth inhibition of five phytopathogenic fungi (Botrytis cinerea, Cochliobolus miyabeanus, Fusarium oxysporum f. sp. cucumerium, Fusarium oxysporum f. sp. niveum, and Phomopsis asparagi) and four marine phytoplankton species (Amphidinium carterae, Heterocapsa circularisquama, Heterosigma akashiwo, and Prorocentrum donghaiense). Several of them exhibited significant inhibitory activities against the fungi and phytoplankton tested of which trichodermin (12) showed the highest antifungal and antimicroalgal activities with MIC and IC50 values being 4.0 and 0.82 µg/mL, respectively.

Septins are required for reproductive propagule development and virulence of the maize pathogen Cochliobolus heterostrophus.

Septins are highly conserved GTP-binding proteins that function in cell cytokinesis, polarity and morphogenesis. To evaluate the roles of these proteins in inoculum health and disease, mutants deleted for each of five septin proteins (Cdc3, Cdc10, Cdc11, Cdc12, and Cdc100) were characterized in the ascomycete Cochliobolus heterostrophus for ability to develop asexual and sexual spores and for virulence to the host maize. Strains deleted for CDC3, CDC10, CDC11, and CDC12 genes showed significant changes in hyphal growth, and in development of conidia and ascospores compared to the wild-type strain. Conidia had dramatically reduced numbers of septa and rates of germination, while ascospore development was blocked in the meiotic process. Although asci were produced, wild-type ascospores were not. When equal numbers of conidia from wild type and mutants were used to inoculate maize, cdc10 mutants showed reduced virulence compared to the wild-type strain and other mutants. This reduced virulence was demonstrated to be correlated with lower germination rate of cdc10 mutant conidia. When adjusted for germination rate, virulence was equivalent to the wild-type strain. Double mutants (cdc3cdc10, cdc3cdc11) showed augmented reduced growth phenotypes. cdc100 mutants were wild type in all assays. Taken together, these findings indicate that all four conserved septin proteins play a major role in reproductive propagule formation and that mutants with deletions of CDC10 are reduced in virulence to the host maize.