Trichoderma atroviride PHR1, a fungal photolyase responsible for DNA repair, autoregulates its own photoinduction

The photolyases, DNA repair enzymes that use visible and long-wavelength UV light to repair cyclobutane pyrimidine dimers (CPDs) created by short-wavelength UV, belong to the larger photolyase-cryptochrome gene family. Cryptochromes (UVA-blue light photoreceptors) lack repair activity, and sensory and regulatory roles have been defined for them in plants and animals. Evolutionary considerations indicate that cryptochromes diverged from CPD photolyases before the emergence of eukaryotes. In prokaryotes and lower eukaryotes, some photolyases might have photosensory functions. phr1 codes for a class I CPD photolyase in Trichoderma atroviride. phr1 is rapidly induced by blue and UVA light, and its photoinduction requires functional blue light regulator (BLR) proteins, which are White Collar homologs in Trichoderma. Here we show that deletion of phr1 abolished photoreactivation of UVC (200 to 280 nm)-inhibited spores and thus that PHR1 is the main component of the photorepair system. The 2-kb 5' upstream region of phr1, with putative light-regulated elements, confers blue light regulation on a reporter gene. To assess phr1 photosensory function, fluence response curves of this light-regulated promoter were tested in null mutant (Deltaphr1) strains. Photoinduction of the phr1 promoter in Deltaphr1 strains was >5-fold more sensitive to light than that in the wild type, whereas in PHR1-overexpressing lines the sensitivity to light increased about 2-fold. Our data suggest that PHR1 may regulate its expression in a light-dependent manner, perhaps through negative modulation of the BLR proteins. This is the first evidence for a regulatory role of photolyase, a role usually attributed to cryptochromes.     

Carbon source dependence and photostimulation of conidiation in Hypocrea atroviridis

Hypocrea atroviridis is frequently used as a photomorphogenetic model due to its ability to conidiate upon exposure to light. Light is thereby believed to be the primary trigger for spore formation. In contrast, we show here that conidiation is primarily carbon source dependent and that illumination plays a catalytic role; of a total of 95 tested carbon sources, only a small set of carbohydrates, polyols, and sugar acids allowed conidiation in darkness, and on most of them, conidiation was significantly more strongly expressed in light. In addition, there are also a number of carbon sources on which H. atroviridis conidiates in darkness, but light does not further stimulate the process. Yet on another small set of carbon sources (L-sorbitol, D-fucose, D- and L-arabinose, and erythritol), H. atroviridis shows better sporulation in darkness than in light. No sporulation was observed on organic acids and amino acids. Mutants with deletions in the two blue-light receptor proteins BLR-1 and BLR-2 generally showed weaker conidiation on a smaller number of carbon sources than did the parental strain, yet they clearly sporulated on 15 and 27 of the 95 carbon sources tested, respectively. Of the carbon sources supporting sporulation, only 11 supported the conidiation of both mutants, suggesting that the BLR-1 and BLR-2 receptors are variously involved in the carbon source-dependent regulation of spore formation. The addition of cyclic AMP, which has been reported to lead to conidiation in darkness, both positively and negatively affected sporulation and resulted in different effects in the parental strain and the two Deltablr mutants. Our data show that the carbon source is the prime determinant for conidiation and that it influences the organism's regulation of conidiation by means of BLR-1 and BLR-2 and their cross talk with cyclic AMP.     

Rhythmic conidiation in the blue-light fungus Trichoderma pleuroticola

Trichoderma species conidiate in response to blue light, however, unlike in the blue-light model fungus Neurospora crassa, conidiation in Trichoderma spp. has been considered to be non-circadian. In this study we uncovered evidence for circadian conidiation in Trichoderma pleuroticola and identified orthologues of the key N. crassa clock components, wc-1 (blr-1) and frq.     

cry1 and GPA1 signaling genetically interact in hook opening and anthocyanin synthesis in Arabidopsis

While studying blue light-independent effects of cryptochrome 1 (cry1) photoreceptor, we observed premature opening of the hook in cry1 mutants grown in complete darkness, a phenotype that resembles the one described for the heterotrimeric G-protein α subunit (GPA1) null mutant gpa1. Both cry1 and gpa1 also showed reduced accumulation of anthocyanin under blue light. These convergent gpa1 and cry1 phenotypes required the presence of sucrose in the growth media and were not additive in the cry1 gpa1 double mutant, suggesting context-dependent signaling convergence between cry1 and GPA1 signaling pathways. Both, gpa1 and cry1 mutants showed reduced GTP-binding activity. The cry1 mutant showed wild-type levels of GPA1 mRNA or GPA1 protein. However, an anti-transducin antibody (AS/7) typically used for plant Gα proteins, recognized a 54?kDa band in the wild type but not in gpa1 and cry1 mutants. We propose a model where cry1-mediated post-translational modification of GPA1 alters its GTP-binding activity.     

Short Communication: Photoinduced sporulation in Trichoderma harzianum–an experimental approach to primary events

Photoinduced sporulation in Trichoderma harzianum could be achieved in the dark in the presence of hydrogen peroxide. However, methylene blue could induce sporulation in red light. Acetylcholine in the presence of eserine when supplied exogenously could mimic blue light effects in complete darkness. Immediate changes in external pH after acetylcholine/eserine treatment were found to be the same as in the blue light induction.     

Circadian rhythmicity in the expression of a novel light-regulated rice gene

We have identified and analyzed cDNAs corresponding to a single-copy gene from rice, designated lir1, whose expression exhibits dramatic diurnal fluctuations. The cDNAs encode a putative protein of 128 amino acids with no homology to known proteins. Lir1 mRNA accumulates in the light, reaching maximum and minimum steady-state levels at the end of the light and dark period, respectively. The oscillations of lir1 mRNA abundance persist after the plants have been transferred to continuous light or darkness. Plants germinated in the dark have very low levels of lir1 mRNA, whereas plants germinated in continuous light express lir1 at an intermediate but constant level. These results indicate that lir1 expression is controlled by light and a circadian clock.     

Light-quality and irradiance effects on pigments, light-harvesting proteins and Rubisco activity in a chlorophyll- and light- harvesting-deficient soybean mutant

Soybean ( Glycine max [L.] Merrill) plants, normal green (Clark L1) and mutant yellow (Clark y₉y₉), were grown in (1) full-spectrum solar irradiation; (2) either red plus far-red or blue plus far-red; (3) either red or blue light with no far-red light. Young leaves harvested from first (1TF) trifoliolate or fifth (5TF) trifoliolate stages of development showed that the mutant plants express pigment and protein deficiencies as a direct function of irradiance. Response of the mutant to light quality indicates that blue light slightly enhances expression of the mutation at higher irradiances. Direct response of light-harvesting proteins of photosystem 2 (LHCP2) and light-harvesting protein of photosystem 1 (LHCP1) to light quality increases the ratio of LHCP1/LHCP2 in blue light compared to that in red or red/far-red light. Rubisco proteins and Rubisco activity (leaf area basis) are directly related to irradiance level but are enhanced in blue light over equal irradiance red. This enhancement is not shown in the presence of far-red light.