Identification of Cyclocybe erebia metabolites that affect the circadian rhythm of Eluc expression under control of Bmal1 promoter in mouse fibroblast cells.

Pharmacological intervention of circadian rhythms is a potentially useful approach for ameliorating various health problems caused by disturbed circadian rhythms including sleep disorder and metabolic diseases. To find compounds that affect circadian rhythms, we screened mushroom extracts using mouse cells expressing the luciferase gene under the control of the mouse Bmal1 promoter. The culture filtrate extract from the basidiomycete Cyclocybe erebia enhanced the oscillation of bioluminescence caused by the expression of the luciferase gene and prolonged the period of bioluminescence. Bioassay-guided fractionation of the extract resulted in purification of compounds 1 and 2. Spectroscopic analyses along with single-crystal X-ray diffraction analysis, revealed that these compounds were diterpenoids with a unique skeleton and a fused ring system comprising 3-, 7-, and 5-membered rings. Compounds 1 and 2 were named cyclocircadins A and B, respectively. These findings suggested that natural diterpenoids could be a source of compounds with the activity affecting circadian rhythms.

Mutations Found in the Asc1 Gene That Confer Susceptibility to the AAL-Toxin in Ancestral Tomatoes from Peru and Mexico.

Tomato susceptibility/resistance to stem canker disease caused by Alternaria alternata f. sp. lycopersici and its pathogenic factor AAL-toxin is determined by the presence of the Asc1 gene. Several cultivars of commercial tomato (Solanum lycopersicum var. lycopersicum, SLL) are reported to have a mutation in Asc1, resulting in their susceptibility to AAL-toxin. We evaluated 119 ancestral tomato accessions including S. pimpinellifolium (SP), S. lycopersicum var. cerasiforme (SLC) and S. lycopersicum var. lycopersicum "jitomate criollo" (SLJ) for AAL-toxin susceptibility. Three accessions, SP PER018805, SLC PER018894, and SLJ M5-3, were susceptible to AAL-toxin. SLC PER018894 and SLJ M5-3 had a two-nucleotide deletion (nt 854_855del) in Asc1 identical to that found in SLL cv. Aichi-first. Another mutation (nt 931_932insT) that may confer AAL-toxin susceptibility was identified in SP PER018805. In the phylogenetic tree based on the 18 COSII sequences, a clade (S3) is composed of SP, including the AAL-toxin susceptible PER018805, and SLC. AAL-toxin susceptible SLC PER018894 and SLJ M5-3 were in Clade S2 with SLL cultivars. As SLC is thought to be the ancestor of SLL, and SLJ is an intermediate tomato between SLC and SLL, Asc1s with/without the mutation seem to have been inherited throughout the history of tomato domestication and breeding.

Clues to an Evolutionary Mystery: The Genes for T-Toxin, Enabler of the Devastating 1970 Southern Corn Leaf Blight Epidemic, Are Present in Ancestral Species, Suggesting an Ancient Origin.

The Southern corn leaf blight (SCLB) epidemic of 1970 devastated fields of T-cytoplasm corn planted in monoculture throughout the eastern United States. The epidemic was driven by race T, a previously unseen race of Cochliobolus heterostrophus. A second fungus, Phyllosticta zeae-maydis, with the same biological specificity, appeared coincidentally. Race T produces T-toxin, while Phyllosticta zeae-maydis produces PM-toxin, both host-selective polyketide toxins necessary for supervirulence. The present abundance of genome sequences offers an opportunity to tackle the evolutionary origins of T- and PM- toxin biosynthetic genes, previously thought unique to these species. Using the C. heterostrophus genes as probes, we identified orthologs in six additional Dothideomycete and three Eurotiomycete species. In stark contrast to the genetically fragmented race T Tox1 locus that encodes these genes, all newly found Tox1-like genes in other species reside at a single collinear locus. This compact arrangement, phylogenetic analyses, comparisons of Tox1 protein tree topology to a species tree, and Tox1 gene characteristics suggest that the locus is ancient and that some species, including C. heterostrophus, gained Tox1 by horizontal gene transfer. C. heterostrophus and Phyllosticta zeae-maydis did not exchange Tox1 DNA at the time of the SCLB epidemic, but how they acquired Tox1 remains uncertain. The presence of additional genes in Tox1-like clusters of other species, although not in C. heterostrophus and Phyllosticta zeae-maydis, suggests that the metabolites produced differ from T- and PM-toxin.

Host-selective toxins produced by the plant pathogenic fungus Alternaria alternata.

Host-selective toxins (HSTs) produced by fungal plant pathogens are generally low-molecular-weight secondary metabolites with a diverse range of structures that function as effectors controlling pathogenicity or virulence in certain plant-pathogen interactions. There are now seven known diseases caused by Alternaria alternata in which HSTs are responsible for fungal pathogenesis. The pathogens have been defined as pathotypes of A. alternata because of morphological similarity but pathological differences. Chemical structures of HSTs from six pathotypes have been determined. The role of A. alternata HSTs in pathogenesis has been studied extensively, and discovery of the release of HSTs from germinating conidia prior to penetration aids in understanding the early participation of HSTs to induce susceptibility of host cells by suppressing their defence reactions. Many attempts have been made to find the target sites of A. alternata HSTs, and four cellular components, plasma membrane, mitochondrion, chloroplast and a metabolically important enzyme, have been identified as the primary sites of each HST action, leading to elucidation of the molecular mechanisms of HST sensitivity in host plants. Studies of the molecular genetics of HST production have identified supernumerary chromosomes encoding HST gene clusters and have provided new insights into the evolution of A. alternata pathotypes.

Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus.

The tomato pathotype of Alternaria alternata produces host-specific AAL toxin and causes Alternaria stem canker on tomato. A polyketide synthetase (PKS) gene, ALT1, which is involved in AAL toxin biosynthesis, resides on a 1.0-Mb conditionally dispensable chromosome (CDC) found only in the pathogenic and AAL toxin-producing strains. Genomic sequences of ALT1 and another PKS gene, both of which reside on the CDC in the tomato pathotype strains, were compared to those of tomato pathotype strains collected worldwide. This revealed that the sequences of both CDC genes were identical among five A. alternata tomato pathotype strains having different geographical origins. On the other hand, the sequences of other genes located on chromosomes other than the CDC are not identical in each strain, indicating that the origin of the CDC might be different from that of other chromosomes in the tomato pathotype. Telomere fingerprinting and restriction fragment length polymorphism analyses of the A. alternata strains also indicated that the CDCs in the tomato pathotype strains were identical, although the genetic backgrounds of the strains differed. A hybrid strain between two different pathotypes was shown to harbor the CDCs derived from both parental strains with an expanded range of pathogenicity, indicating that CDCs can be transmitted from one strain to another and stably maintained in the new genome. We propose a hypothesis whereby the ability to produce AAL toxin and to infect a plant could potentially be distributed among A. alternata strains by horizontal transfer of an entire pathogenicity chromosome. This could provide a possible mechanism by which new pathogens arise in nature.