The Translation Inhibitor Rocaglamide Targets a Bimolecular Cavity between eIF4A and Polypurine RNA.

A class of translation inhibitors, exemplified by the natural product rocaglamide A (RocA), isolated from Aglaia genus plants, exhibits antitumor activity by clamping eukaryotic translation initiation factor 4A (eIF4A) onto polypurine sequences in mRNAs. This unusual inhibitory mechanism raises the question of how the drug imposes sequence selectivity onto a general translation factor. Here, we determined the crystal structure of the human eIF4A1⋅ATP analog⋅RocA⋅polypurine RNA complex. RocA targets the "bi-molecular cavity" formed characteristically by eIF4A1 and a sharply bent pair of consecutive purines in the RNA. Natural amino acid substitutions found in Aglaia eIF4As changed the cavity shape, leading to RocA resistance. This study provides an example of an RNA-sequence-selective interfacial inhibitor fitting into the space shaped cooperatively by protein and RNA with specific sequences.

An evaluation of taxonomic concepts of the widespread plant genus Aglaia and its allies across Wallace's Line (tribe Aglaieae, Meliaceae).

Similar to other species-rich taxa in the Indo-Australian Archipelago, taxonomy of the genus Aglaia (mahogany family, Meliaceae) remains problematic. This study aims to evaluate taxonomic concepts within Aglaia based on the largest dataset to-date. We analyzed sequences of 237 accessions of Aglaia and representatives of all other genera of the tribe Aglaieae, including nuclear ribosomal ITS, the trnL-trnF intron and intergenic spacer, the atpF intron and the petD region comprising the petB-petD spacer, the petD-5' exon and the petD intron (all but the first from the plastid genome). Our analyses were set both in maximum likelihood and Bayesian frameworks, which (1) supported paraphyly of Aglaia and Aphanamixis; (2) demonstrated polyphyly of previously described sections for Aglaia; and (3) suggested delimitation problems with 57% of the morphologically "variable species" and all "complex species". In general, there were more genetic entities than species described, which shows that the taxonomy of this group is more complex than has sometimes been previously assumed. For some species, morphological variation suggests the existence of more variants, subspecies or species within various taxa. Furthermore, our study detected additional phylogenetic entities that were geographically distinct, occurring on either side of Wallace's Line but not on both sides. The delineation of these inter-specific taxa needs further investigation by taking into account the morphological variation within and between populations across the entire distribution.

Internal transcribed spacer 2 (ITS2) molecular morphometric analysis based species delimitation of foliar endophytic fungi from Aglaia elaeagnoidea, Flacourtia inermis and Premna serratifolia.

Molecular morphometrics is an emerging third dimensional aspect of fungal species delimitation. They have been demonstrated to be more informative than conventional barcoding methods. Hence in this study, foliar endophytic fungal (FEF) assemblages in three Magnoliopsida plants were delimited using nuclear ribosomal internal transcribed spacer 2 (ITS2) sequence-secondary structural features based phylogenetic analysis, also known as molecular morphometrics. A total of 392 FEF isolates were obtained from the Aglaia elaeagnoidea, Flacourtia inermis, and Premna serratifolia leaves and grouped into 98 morphotypes. Among these host plants, P. serratifolia showed the maximum percentage of colonization frequency. Representatives of each morphotype was sequenced and subjected to further molecular characterization. The results revealed that morphotypes were belonged to the phylum of Ascomycota, distributed over two classes (Sordariomycetes (68.59%) and Dothideomycetes (31.41%)), 6 orders and 19 genera. Based on compensatory base changes (CBC) analysis and absolute identity of ITS2 structure, 21, 20 and 23 species were recognized from A. elaeagnoidea, F. inermis, and P. serratifolia respectively. Diversity indices were higher in A. elaeagnoidea, despite it accounted for a modest 16.8% of total isolates recorded in this study. The genus Colletotrichum was predominant in A. elaeagnoidea (39%) and P. serratifolia (48%). Similarly, Diaporthe (43%) was dominant in F. inermis. Several host-specific species were also observed. This study concludes that these plants host diverse species of Ascomycota. To the best of our knowledge, this is the first detailed report on FEF diversity from these plants. Also, the inclusion of ITS2 secondary structure information along with the sequence provides a further dimension to resolve the inherent problems in identification of fungal species.

A nucleotide signature for identification of Aglaia stellatopilosa Pannell.

Members of the genus Aglaia have been reported to contain bioactive phytochemicals. The genus, belonging to the Meliaceae family, is represented by at least 120 known species of woody trees or shrubs in the tropical rain forest. As some of these species are very similar in their morphology, taxonomic identification can be difficult. A reliable and definitive molecular method which can identify Aglaia to the level of the species will hence be useful in comparing the content of specific bioactive compounds between the species of this genus. Here, we report the analysis of DNA sequences in the internal transcribed spacer (ITS) of the nuclear ribosomal DNA and the observation of a unique nucleotide signature in the ITS that can be used for the identification of Aglaia stellatopilosa. The nucleotide signature consists of nine bases over the length of the ITS sequence (654 bp). This uniqueness was validated in 37 samples identified as Aglaia stellatopilosa by an expert taxonomist, whereas the nucleotide signature was lacking in a selection of other Aglaia species and non-Aglaia genera. This finding suggests that molecular typing could be utilized in the identification of Aglaia stellatopilosa.