Visualizing Nuclear Migration during Conidiophore Development inAspergillus nidulansandAspergillus oryzae: Multinucleation of Conidia Occurs through Direct Migration of Plural Nuclei from Phialides and Confers Greater Viability and Early Germination inAspergillus oryzae

Abstract

Nuclear migration is indispensable for normal growth, differentiation, and development, and has been studied in several fungi including Aspergillus nidulans and Neurospora crassa. To better characterize nuclear movement and its consequences during conidiophore development, conidiation, and conidial germination, we performed confocal microscopy and time-lapse imaging on A. nidulans and Aspergillus oryzae strains expressing the histone H2B-EGFP fusion protein. Active trafficking of nuclei from a vesicle to a phialide and subsequently into a conidium provided the mechanistic basis for the formation of multinucleate conidia in A. oryzae. In particular, the first direct visual evidence on multinucleate conidium formation by the migration of nuclei from a phialide into the conidium, rather than by mitotic division in a newly formed conidium, was obtained. Interestingly, a statistical analysis on conidial germination revealed that conidia with more nuclei germinated earlier than those with fewer nuclei. Moreover, multinucleation of conidia conferred greater viability and resistance to UV-irradiation and freezethaw treatment.

Aspergillus terreusaccessory conidia are multinucleated, hyperpolarizing structures that display differential dectin staining and can induce heightened inflammatory responses in a pulmonary model of aspergillosis

“…In A. oryzae, multi-nucleation of conidia conferred greater viability and resistance to UV radiation and freeze-thaw treatment, thus resulting in better adaptation to adverse environmental conditions and could ensure conidial preservation. 24 Although such viability experiments were not performed in the present study, there is some evidence that AC are at least more resistant to antifungal drugs than PC. If indeed multinucleation imparted viability benefits to AC, this would be a significant virulence factor for A. terreus as it would allow the organism to survive the harsh environment of the host during infection.…”

“…Similar to our study, in A. oryzae, multinucleate conidia had a higher germination efficiency than uninucleate conidia. 24 Additionally, late stage germination of both A. terreus PC and AC culminates in production of hyphae on which grow more AC, which in turn polarize in multiple directions to quickly form several more hyphal extensions. In spite of differences in germination potential between the two conidial forms, once both conidia achieved germination, the ensuing chemokine levels were assessed in the supernatants using the Bio-Plex Protein Array System (Bio-Rad, Hercules, California United States) as per the manufacturer's instructions.…”

Characterization of the aodA, dnmA, mnSOD and pimA genes in Aspergillus nidulans

“…S6 ). These observations on asexual and sexual sporulations may also be important when the potential industrial applications of genetically engineered Aspergillus strains are considered 53 .…”

Invasive growth of Aspergillus oryzae in rice koji and increase of nuclear number

“…Since the increase of nuclei in A. oryzae was predicted to be correlated to the high secretion capacity of several enzymes, we focused on the phenotype. The nuclear distribution in A. oryzae has been analyzed in hyphae and especially in conidia (42,43), which indicated multi-nuclear conidia; the number of nuclei in each conidium varied from 1 to 7 in A. oryzae strains used in sake brewing. We investigated the nuclear distribution in A. oryzae hyphae grown in detail by using the minimal medium but not the rice koji.…”