Genome-Wide Identification and Expression Analysis of the bZIP Transcription Factors in the Mycoparasite Coniothyrium minitans

The basic leucine zipper (bZIP) proteins family is one of the largest and most diverse transcription factors, widely distributed in eukaryotes. However, no information is available regarding the bZIP gene family in Coniothyrium minitans, an important biocontrol agent of the plant pathogen Sclerotinia sclerotiorum. In this study, we identified 34 bZIP genes from the C. minitans genome, which were classified into 8 groups based on their phylogenetic relationships. Intron analysis showed that 28 CmbZIP genes harbored a variable number of introns, and 15 of them shared a feature that intron inserted into the bZIP domain. The intron position in bZIP domain was highly conserved, which was related to recognize the arginine (R) and could be treated as a genomic imprinting. Expression analysis of the CmbZIP genes in response to abiotic stresses indicated that they might play distinct roles in abiotic stress responses. Results showed that 22 CmbZIP genes were upregulated during the later stage of conidial development. Furthermore, transcriptome analysis indicated that CmbZIP genes are involved in different stages of mycoparasitism. Among deletion mutants of four CmbZIPs (CmbZIP07, -09, -13, and -16), only ΔCmbZIP16 mutants significantly reduced its tolerance to the oxidative stress. The other mutants exhibited no significant effects on colony morphology, mycelial growth, conidiation, and mycoparasitism. Taken together, our results suggested that CmbZIP genes play important roles in the abiotic stress responses, conidial development, and mycoparasitism. These results provide comprehensive information of the CmbZIP gene family and lay the foundation for further research on the bZIP gene family regarding their biological functions and evolutionary history.

Differences in early hyphal development of Podosphaera xanthii on Cucumis sativus leaves acclimatized to high or low relative humidity

This research investigated early hyphal development of cucurbit powdery mildew (Podosphaera xanthii) on leaves of cucumber (Cucumis sativus L.) acclimatized to different relative humidities to clarify the factors that limit it. Cucumber seedlings were acclimatized to a low (10%) or high (90%) relative humidity (RH) at 30 °C from germination. When the cotyledons had expanded and the first true leaf had begun to emerge, the plants were inoculated, and initial conidial invasion, hyphal development, and secondary haustorial formation were evaluated. The initial invasion of P. xanthii into the epidermis was slower on the low-RH leaves than on the high-RH leaves, suggesting that structural properties, such as greater leaf mass per area, physically limited the development of P. xanthii. The hyphal development and secondary haustoria of conidia that had successfully infected the epidermis were also slower on the low-RH leaves. These post-invasion behaviors indicate that conidial development was also suppressed by nonstructural properties of low-RH leaves such as nutrients, which correlate with nonstructural defense. The reduced leaf N content of the low-RH leaves may in part have inhibited the post-invasion behaviors of P. xanthii.

Development of Colletotrichum acutatum in the foliar tissue of strawberry plants

Strawberry anthracnose, caused by Colletotrichum acutatum, is one of the most destructive disease of this crop throughout the world. Assymptomatic stages in the plant have been the aim of this work. Inoculated leaves samples were taken at different times and they were processed for scanner electron microscopy (SEM) and transmission electron microscopy (TEM). Conidial development on both surfaces leaves was determined. The ultrastructural study of fungus penetration into plant cell was characterized by the formation of vesicles over the fungus periphery and is a morphological parameter of the intense membranes traffic, also could be a evidence of a transcriptional activity and enzymatic cell secretion. Differences of symptoms on both surfaces of leaves were observed.

Fungi associated with hibernating bats in New Brunswick caves: the genus Leuconeurospora

Two species of Leuconeurospora, Leuconeurospora capsici (J.F.H. Beyma) Malloch, Sigler & Hambleton and Leuconeurospora polypaeciloides Malloch, Sigler & Hambleton (Ascomycota: Pseudeurotiaceae), are reported from the fur and skin of hibernating bats and from other substrata in caves in New Brunswick, Canada. Separate analyses using ITS, RPB1, and RPB2 DNA sequence data are in agreement and show these two species and the type species, Leuconeurospora pulcherrima (G. Winter) Malloch & Cain, form discrete clades within a distinct Leuconeurospora clade. The three species are distinguishable morphologically by their anamorphs, having dark conidia in L. capsici, hyaline conidia in L. polypaeciloides, and no conidia in L. pulcherrima. Ascomata and ascospores are produced in L. pulcherrima and in mated isolates of L. polypaeciloides, but have not been observed in L. capsici. Leuconeurospora species are psychrotolerant, with faster growth and heavier conidial development at 7 °C than at 22 °C. Of 151 bats sampled from 10 caves, 51 yielded isolates of L. polypaeciloides and 15 yielded L. capsici. The results were not uniform: neither species was isolated from bats in three caves, while three caves yielded isolates of both species and two yielded L. polypaeciloides only. These species were also isolated from cave walls and arthropods in the cave.

Early Development of Powdery Mildew on Cucumber Leaves Acclimatized to Illumination with Different Red-to-far-red Ratios

The development of powdery mildew fungus (Podosphaera xanthii) is suppressed on cucumber (Cucumis sativus L.) seedlings acclimatized to higher red-to-far-red ratio (R:FR) than natural R:FR (≈1.2), but its early development and any limiting factors are still unclear. The present study evaluated conidial germination, initial invasion, and subsequent development of P. xanthii on cucumber seedlings raised under light-emitting diode (LED) lights with R:FRs of 1.2, 5.0, or 10. There were no differences in conidial germination or initial invasion between the treatments, so there was no effect of acclimatization to R:FR on either. But, the development of hyphae, hyphal cells, and haustoria after inoculation were suppressed on seedlings acclimatized to higher R:FR. Because differences occurred only after the initial invasion, nonstructural properties of the host leaves may have affected conidial development. Higher R:FR also suppressed conidial development under natural light filtered through a photo-selective film, which absorbs near-infrared (NIR)-light. However, this effect was reduced when the plants were moved to natural R:FR after inoculation, possibly because of reacclimatization of the seedlings.

Deletion of the Aspergillus flavus Orthologue ofA. nidulans fluGReduces Conidiation and Promotes Production of Sclerotia but Does Not Abolish Aflatoxin Biosynthesis

ABSTRACTThefluGgene is a member of a family of genes required for conidiation and sterigmatocystin production inAspergillus nidulans. We examined the role of theAspergillus flavus fluGorthologue in asexual development and aflatoxin biosynthesis. Deletion offluGinA. flavusyielded strains with an approximately 3-fold reduction in conidiation but a 30-fold increase in sclerotial formation when grown on potato dextrose agar in the dark. The concurrent developmental changes suggest thatA. flavusFluG exerts opposite effects on a mutual signaling pathway for both processes. The altered conidial development was in part attributable to delayed expression ofbrlA, a gene controlling conidiophore formation. Unlike the loss of sterigmatocystin production byA. nidulans fluGdeletion strains, aflatoxin biosynthesis was not affected by thefluGdeletion inA. flavus. InA. nidulans, FluG was recently found to be involved in the formation of dehydroaustinol, a component of a diffusible signal of conidiation. Coculturing experiments did not show a similar diffusible meroterpenoid secondary metabolite produced byA. flavus. These results suggest that the function offluGand the signaling pathways related to conidiation are different in the two related aspergilli.