The DNA damage sensor XPC is involved in nucleotide excision repair. Here we show that in the absence of damage, XPC co-localizes with RNA polymerase II (Pol II) and active post-translational histone modifications marks on a subset of class II promoters in human fibroblasts. XPC depletion triggers specific gene down-expression due to a drop in the deposition of histone H3K9 acetylation mark and pre-initiation complex formation. XPC interacts with the histone acetyltransferase KAT2A and specifically triggers the recruitment of the KAT2A-containing ATAC complex to the promoters of down-expressed genes. We show that a strong E2F1 signature characterizes the XPC/KAT2A-bound promoters and that XPC interacts with E2F1 and promotes its binding to its DNA element. Our data reveal that the DNA repair factor XPC is also an RNA polymerase II cofactor recruiting the ATAC coactivator complex to promoters by interacting with the DNA binding transcription factor E2F1.

Cytokinins (CKs) and ethylene (ET) are among the most ancient organic chemicals on Earth. A wide range of organisms including plants, algae, fungi, amoebae, and bacteria use these substances as signaling molecules to regulate cellular processes. Because of their ancestral origin and ubiquitous occurrence, CKs and ET are also considered to be ideal molecules for inter-kingdom communication. Their signal transduction pathways were first historically deciphered in plants and are related to the two-component systems, using histidine kinases as primary sensors. Paradoxically, although CKs and ET serve as signaling molecules in different kingdoms, it has been supposed for a long time that the canonical CK and ET signaling pathways are restricted to terrestrial plants. These considerations have now been called into question following the identification over recent years of genes encoding CK and ET receptor homologs in many other lineages within the tree of life. These advances shed new light on the dissemination and evolution of these hormones as both intra- and inter-specific communication molecules in prokaryotic and eukaryotic organisms.

Although it has long been known that bacteria detect and react to plant chemicals to establish an interaction, the cellular signaling mechanisms involved in these perception processes have hitherto remained obscure. Some exciting recent advances in the field have described, for the first time, how some phytopathogenic bacteria sense the host plant hormones, cytokinins. These discoveries not only advance the understanding of cell signaling circuitries engaged in cytokinin sensing in non-plant organisms, but also increase our knowledge of the broad role of these ancient molecules in regulating intra- and interspecific communications.

Aim: We sought to provide first insights into the epidemiology and antifungal susceptibility patterns of the aspergilli in Lebanon. Materials & methods: After species identification, antifungal sus...

Signals are exchanged at all stages of the arbuscular mycorrhizal (AM) symbiosis between fungi and their host plants. Root-exuded strigolactones are well-known early symbiotic cues, but the role of other phytohormones as interkingdom signals has seldom been investigated. Here we focus on ethylene and cytokinins, for which candidate receptors have been identified in the genome of the AM fungus Rhizophagus irregularis. Ethylene is known from the literature to affect asymbiotic development of AM fungi, and in the present study, we found that three cytokinin forms could stimulate spore germination in R. irregularis. Heterologous complementation of a Saccharomyces cerevisiae mutant strain with the candidate ethylene receptor RiHHK6 suggested that this protein can sense and transduce an ethylene signal. Accordingly, its N-terminal domain expressed in Pichia pastoris displayed saturable binding to radiolabeled ethylene. Thus, RiHHK6 displays the expected characteristics of an ethylene receptor. In contrast, the candidate cytokinin receptor RiHHK7 did not complement the S. cerevisiae mutant strain or Medicago truncatula cytokinin receptor mutants and seemed unable to bind cytokinins, suggesting that another receptor is involved in the perception of these phytohormones. Taken together, our results support the hypothesis that AM fungi respond to a range of phytohormones and that these compounds bear multiple functions in the rhizosphere beyond their known roles as internal plant developmental regulators. Our analysis of two phytohormone receptor candidates also sheds new light on the possible perception mechanisms in AM fungi.

Like bacteria and plants, fungi produce a remarkable diversity of small molecules with potent activities for human health known as natural products or secondary metabolites. One such example is mycophenolic acid, a powerful immunosuppressant drug that is administered daily to millions of transplant recipients worldwide. Production of mycophenolic acid is restricted to a very limited number of filamentous fungi, and little is known about its biosynthetic modalities. It is therefore a particular challenge to improve our knowledge of the biosynthesis of this valuable natural compound, as this would contribute to a better understanding of the specialized metabolism of fungi and could also lead to the identification of new fungal producers for the supply of immunosuppressants. Here, we were interested in deciphering the origin and evolution of the fungal mycophenolic acid biosynthetic pathway. Large-scale analyses of fungal genomic resources led us to identify several new species that harbor a gene cluster for mycophenolic acid biosynthesis. Phylogenomic analysis suggests that the mycophenolic acid biosynthetic gene cluster originated early in a common ancestor of the fungal family Aspergillaceae but was repeatedly lost and it is now present in a narrow but diverse set of filamentous fungi. Moreover, a comparison of the inosine 5′-monophosphate dehydrogenase protein sequences that are the target of the mycophenolic acid drug as well as analysis of mycophenolic acid production and susceptibility suggest that all mycophenolic acid fungal producers are resistant to this toxic compound, but that this resistance is likely to be based on different molecular mechanisms. Our study provides new insight into the evolution of the biosynthesis of the important secondary metabolite mycophenolic acid in fungi.