Neurospora sees the light: light signaling components in a model system

Abstract

Light is a key environmental signal for most life on earth. Over 5% of Neurospora crassa genes are expressed in response to light stimulation in a temporally regulated cascade that includes several transcription factors. Fungal genomes, including Neurospora's, may encode several different proteins capable of binding chromophores with the ability to harvest light energy as well as proteins that can interact with primary photoreceptors or further propogate the light signal. The best understood photo- receptors are the evolutionarily conserved White Collar proteins, and the related Vivid protein, but fungi may also encode phytochromes, cryptochromes and opsins.

Keywords: Neurospora; frq; light; microarray; nop-1; photoreceptors; sub-1; ve-1; vvd; wc-1; wc-2.

Figure 1

Established and putative molecular components involved in Neurospora light signaling. WC-1 and WC-2 form a heterodimeric transcription factor (WCC) that binds to early light responsive elements (ELREs). In response to a light signal, transcription is rapidly activated, resulting in the expression of several downstream transcription factors, as well as the VVD and FRQ proteins. The SUB-1 transcription factor is required for expression of most late-light responsive genes, many of which have a specific late light responsive element (LLRE), A/GTGAC/TG/ATCA. VVD acts as a potent repressor of WCC activity on light regulated genes. FRQ may block further activity on some genes while at the same time promotes expression of the WCC. Several proteins can bind chromophores (WC-1, PHY-1, NOP-1, VVD, CRY and maybe PHY-2). Chromophores are shown as stars in the color of light they absorb. Several proteins have no described responses to light in Neurospora (CRY, PHY-1, PHY-2, VE-1) although they do in other fungi and other organisms.