Photoperiodic Responses and Characterization of the Cmvvd Gene Encoding a Blue Light Photoreceptor from the Medicinal Caterpillar Fungus Cordyceps militaris (Ascomycetes).

Abstract

Light is a necessary environmental factor for production of conidia and pigment, formation of stroma, and development of Cordyceps militaris, a well-known edible and medicinal mushroom. In this study, an obvious rhythm loop was observed in certain strains of C. militaris under conditions of alternating 12-hour intervals of dark and light. A possibly related gene, Cmvvd, the homologue of the blue-light photoreceptor of Neurospora crassa, was cloned from the genome of C. militaris. The protein CmVVD is predicted to be 203 amino acids in length and is characterized by the presence of a light, oxygen, or voltage domain. Analysis of the CmVVD sensor domain (light, oxygen, or voltage) suggested that it is a blue-light receptor. Cysteine 108 is essential for the in vivo function of VIVID (VVD) in N. crassa photoadaptation. However, proline is in this position instead in all of the tested CmVVD proteins, suggesting that CmVVD may have a different function or may function in ways different from VVD in N. crassa. Genetic variation analysis of CmVVD in 6 representative strains indicated that 3 informative sites exist. Cmvvd messenger RNA was able to be induced by light, and the expression level increased over 10 times after irradiation and was maintained at high levels in the nascent fruiting body. The light-induced expression of Cmvvd was abolished in Cmwc-1 mutants, suggesting that the expression of Cmvvd is dependent on the photoreceptor CmWC-1 or on a functional CmWC-1/WC-2 complex. This article will help to open the still-unexplored field of circadian rhythms for this fungus.