The Mycelium Connection

Just picture the soft blue light glimmering off some well developed stroma, strong mycelial growth subtly reaching out with its probing filaments. Some sexual reproduction is going down today.

Now think of what it is like after that blue light so embodying of the twilight hour stays all the time, or never comes around at all. The light becomes harsh, showing off your conidiation, it is easy to see why stroma can't perform under such... revealing exposure. And while the velvet darkness can seem alluring, a constant darkness causes its own lack of enthusiasm, things may happen but the excitement oft isn't there, so it takes a while longer.

Hypocrea jecorina sporting
some sweet filamentous growth.

Or at least that is what a new study in PLOS One says regarding the sexual development of Hypocrea jecorina under a variety of light exposure growth regimes demonstrates.

Blue Light Acts as a Double-Edged Sword in Regulating Sexual Development of Hypocrea jecorina (Trichoderma reesei)

Light is important to the sexual development of many fungi. Take Neurospora crassa, it has a complex of photoreceptive proteins (the white-collar complex) that directly initiate and manage sexual reproduction. However; the equivalent complexes found in H. jecorina, the blue-light photoreceptors (BLR1 & BLR2), regulate blue-light-induced mycelial growth and cellulase gene expression and the photoadaption protein ENV1 regulates the mycelial growth and tones down the detection of light change, which helps promote sexual development by inhibiting asexual conidiation. Basically that means BLR 1&2 and ENV1 play mainly regulatory roles and are not necessarily essential for sexual reproduction.

To test whether visible light, and thus these photoreceptors, is required by the fungus for a sexually reproductive path, the researchers grew (on malt extract agar plates) H. jecorina under three separate light regimes; 24 hours of light a day, a 12 hour light/12 hours dark day, and a 24 hours of darkness day.

The monitoring revealed that even after 30 days, the strains grown under a full 24 hour light day showed no stroma growth. This means all that total illumination inhibited the sexual development of H. jecorina. Those growing with the balanced 12hr Light/ 12hr Dark days? They knew what was going on ;-). They had a solid mycelial growth with well developed stromata being observed in just 7-9 days. However, when we jump back over to the fungi grown under total darkness, we see stromata form, but they do so more slowly. Also the stroma of the 12L/12D strains showed surface growth of perithecia (A flask shaped fruiting body that contains the ascospores), while the perithecia developing in the stroma of the 24D samples were embedded deeper toward the interior.

These results demonstrated that different light variation greatly affected the sexual development of H. jecorina. While constant light completely inhibited Stroma formation, total darkness caused a slowdown of their growth as well. The second point explains why it has always been reported that light is required for stroma formation. Basically to induce proper sexual development Hypocrea jecorina there must be light, but it needs to be shut off now and then. Maybe, get a dimmer swith installed and turn on some Marvin Gaye.

Awesome researchers:
Chia-Ling Chen, Hsiao-Che Kuo, Shu-Yu Tung, Paul Wei-Che Hsu, Chih-Li Wang, Christian Seibel, Monika Schmoll, Ruey-Shyang Chen, & Ting-Fang Wang (2012). Blue Light Acts as a Double-Edged Sword in Regulating Sexual Development of Hypocrea jecorina (Trichoderma reesei) PLOS One DOI: 10.1371/journal.pone.0044969

Photo Cred:
US Department of Energy Office of Science via Wiki-Commons