Identification and Characterization of Aspergillus nidulans Mutants Impaired in Asexual Development under Phosphate Stress

Abstract

The transcription factor BrlA plays a central role in the production of asexual spores (conidia) in the fungus Aspergillus nidulans. BrlA levels are controlled by signal transducers known collectively as UDAs. Furthermore, it governs the expression of CDP regulators, which control most of the morphological transitions leading to the production of conidia. In response to the emergence of fungal cells in the air, the main stimulus triggering conidiation, UDA mutants such as the flbB deletant fail to induce brlA expression. Nevertheless, ΔflbB colonies conidiate profusely when they are cultured on a medium containing high H2PO4− concentrations, suggesting that the need for FlbB activity is bypassed. We used this phenotypic trait and an UV-mutagenesis procedure to isolate ΔflbB mutants unable to conidiate under these stress conditions. Transformation of mutant FLIP166 with a wild-type genomic library led to the identification of the putative transcription factor SocA as a multicopy suppressor of the FLIP (Fluffy, aconidial, In Phosphate) phenotype. Deregulation of socA altered both growth and developmental patterns. Sequencing of the FLIP166 genome enabled the identification and characterization of PmtCP282L as the recessive mutant form responsible for the FLIP phenotype. Overall, results validate this strategy for identifying genes/mutations related to the control of conidiation.

Nuclear Ssr4 Is Required for the In Vitro and In Vivo Asexual Cycles and Global Gene Activity of Beauveria bassiana

“…However, the developmental activator genes brlA (BBA_07544), abaA (BBA_00300), wetA (BBA_06126), and vosA (BBA_01023), which are evidently required for conidiation and conidial maturation of B. bassiana (33,34), were markedly upregulated (log 2 R, 6.67 for brlA, 3.38 for abaA, and 1.62 for wetA) or unaffected (vosA). None of the genes encoding signal transducers of the upstream developmental activation pathway required for activation of the critical brlA in A. nidulans (35)(36)(37), namely, flbABCDE (BBA_02968, BBA_06988, BBA_03181, BBA_07259, and BBA_01716, respectively) was differentially expressed although the upstream fluG (BBA_04942) was sharply repressed (log 2 R ϭ -8.35). The transcript changes of these development-required genes provided little insight into the severe conidiation defect of Δssr4 under normal culture conditions.…”

“…Asexual development is critical for the survival and dispersal of a filamentous fungus and genetically controlled by sequential activation of brlA, abaA, and wetA in the central developmental pathway and downstream of vosA (35)(36)(37). The four genes were proven to be required for aerial conidiation and conidial maturation of B. bassiana due to abolished conidiation in the absence of brlA or abaA (34) and greatly reduced (98% or 88%) conidial yield and impaired conidial quality in the absence of wetA or vosA (33).…”

Opposite Nuclear Dynamics of Two FRH-Dominated Frequency Proteins Orchestrate Non-Rhythmic Conidiation in Beauveria bassiana

“…Aerial conidiation is critical for survival and dispersal in host habitats of filamentous fungal pathogens. This process is genetically controlled by the upstream development activation (UDA) pathway comprising signal transducers (FluG and FlbA-E) and the central developmental pathway (CDP) consisting of three sequentially activated genes (brlA, abaA, and wetA) in some filamentous fungi, such as Eurotiales [1] (also reviewed in [2,3]). Beauveria bassiana is a filamentous fungal insect pathogen that undergoes asexual cycle with teleomorph never induced successfully under laboratory conditions and serves as a main source of fungal insecticides and acaricides containing formulated conidia as active ingredients (reviewed in [4,5]).…”

IV. Ikergazte. Nazioarteko ikerketa euskaraz. Kongresuko artikulu bilduma. Zientziak eta Natura Zientzia

“…Hala ere, ikusi da badaudela hainbat estimulu (elikagaien agorketa, argia, edo gatz edo karbohidrato espezifikoen kontzentrazio altuak, besteak beste) ugalketa asexuala bultzatzen dutenak (Etxebeste eta Espeso, 2020). ΔflbB mutantearen kasuan, adibidez, ikusi zen hazkuntza baldintza estandarretan erakusten duen fenotipo akonidiala atzera itzuli daitekeela eta konidiazioa eragin fosfato (H 2 PO 4 -; 0.5-0.65M) kontzentrazio handiko medioan hazten bada (1C irudia) (Otamendi et al, 2019). Honek, UDA bideaz gain, brlA-ren indukziorako bide genetiko alternatiboak egon daitezkeela iradokitzen du (laranjaz 1go irudiko B atalean).…”

“…Ustezko bide alternatibo horietan parte hartzen duten geneak identifikatzeko, Otamendi et al (2019) lanean, fosfatodun (0.65M) kultura medioan fenotipo akonidiala zuten 81 ΔflbB mutante (FLIP, fluffy in phosphate, mutanteak) isolatu ziren mutagenesi bidez (1C irudia). Mutante hauek, flbB genearen delezioaz gain, baldintza hauetan garapen asexuala inhibitzen duen beste mutazio ezezagunen bat dute.…”