ROSEOFLAVIN INHIBITION OF PHOTOCONIDIATION IN A Trichoderma RIBOFLAVIN AUXOTROPH: INDIRECT EVIDENCE FOR FLAVIN REQUIREMENT for PHOTOREACTIONS

Abstract

Roseoflavin, an analog known to compete with riboflavin in Lactobacillus casei, riboflavin‐deficient rats, and fungi, was used to ascertain whether a flavin plays a role as a sensitizing pigment for photomorphogenesis in the fungus Trichoderma. Roseoflavin inhibited blue light induced conidiation of a riboflavin‐requiring auxotroph of Trichoderma. Colonies pre‐incubated with roseoflavin needed six times more light to saturate conidiation. Roseoflavin did not change the dark rate of conidial development indicating that it interfered only with the photoact. A revertant from the riboflavin auxotroph strain was not inhibited by roseoflavin. Simultaneous addition of 10 μM riboflavin prevented inhibition by 6.4 μM roseoflavin. Thus, roseoflavin inhibition is probably specific, possibly replacing riboflavin or one of its metabolites in the light reactions. There was no detectable shift in the action spectrum towards the green where roseoflavin absorbs; thus it did not replace a flavin as an efficient photoreceptor.

Cross Talk between a Fungal Blue-Light Perception System and the Cyclic AMP Signaling Pathway

“…EUKARYOT. CELL been shown that in Trichoderma a sudden carbon deprivation mimics the effect of light by triggering the development of a discrete ring of conidia at the growing edge of a colony (20), we decided to verify whether the BLR proteins played any role in the induction of conidiation by nutrient deprivation by testing this response in the corresponding mutants. Briefly, the wild type, and the ⌬blr-1 and ⌬blr-2 mutant strains were grown for 48 h in MM and then transferred to either nitrogen-or glucose-free MM medium and allowed to grow for a further 24 h in complete darkness (Fig.…”

“…Conidiation in this organism is induced by environmental factors such as light and nutrient depletion. In the laboratory, exposure of a dark-grown colony of Trichoderma to a brief pulse of blue light results in the formation of a ring of dark green conidia at what had been the perimeter of the colony at the time of illumination (20). Another light response described in T. atroviride is the regulation of the expression of the photolyase gene phr-1.…”

BLR-1 and BLR-2, key regulatory elements of photoconidiation and mycelial growth in Trichoderma atroviride

“…Experiments with the riboflavin structural analogue roseoflavin (Horwitz et al, 1984b) also indicate the participation of a flavin as the photoreceptive pigment. Phototropism in higher plants (Thimann & Curry, 1960), photocarotenogenesis in Neurospora crassa (De Fabo et al, 1976), and many other biological responses to blue light, have similar action spectra (Senger, 1980).…”

Electric Currents around Growing Trichoderma Hyphae, before and after Photoinduction of Conidiation

“…A series of nonphotoinducible mutants of Trichoderma is being isolated (8). It may eventually be possible to combine genetics, light triggering, and electrophysiology to find out whether a change in membrane properties is an essential part of the pathway leading to morphogenesis.…”

“…A rapid response to light would help screen for nonsporulating mutants (8) that are clearly not affected in cryptochrome, but are deficient in a later part of the pathway. We chose to measure extracellular electric currents because they may be related to development.…”