Bioscience

Biosynthesis of Destruxins in Metarhizium—Puzzle Solved

Nonribosomal cyclopeptide destruxins were first identified from fungi in 1961. Besides their insecticidal activity, destruxins have also been explored as potential pharmaceuticals to treat cancer, osteoporosis, Alzheimer’s disease and hepatitis B. The genes responsible for their biosynthesis were a longstanding puzzle.? Prof. Wang Chengshu at the Institute of Plant and Physiology and Ecology, Shanghai Institutes for Biological Sciences, CAS, and the co-workers from Shanghai Jiaotong University have solved this issue based on comparative genomic analysis, targeted gene disruptions and substrate feeding assays. They found four clustered genes, i.e. the nonrobiosomal peptide synthetase genes dtxS1, cytochrome P450 DtxS2, aldo-keto reductase gene dtxS3 and aspartic acid decarboxylase gene dtx4, are responsible for the biosynthesis and structure modifications of destruxins in the insect pathogen Metarhizium robertsii. They also demonstrated that destruxins could suppress host both cellular and humoral immune responses to assist fungal propagation in insects. The differing abilities of Metarhizium species to produce toxins is dependent on the presence of the dtxS1 gene cluster and the toxigenic species are capable of killing multiple orders of insects while the non-toxigenic Metarhizium spp. have narrow host ranges. Their study advanced the knowledge of fungal secondary metabolism, the mechanism of fungal entomopathogenicity and will facilitate the development of destruins as bioinsecticides or pharmaceuticals. This work has been published on PNAS, 2012 (http://www.pnas.org/cgi/doi/10.1073/pnas.1115983109).

Modern Human Behaviors and Mechanism of Broad Spectrum Revolution

The last glacial period was vital for the distribution and evolution of early modern humans in Asia. The Shuidonggou Late Paleolithic site in Ningxia Province, accumulated cultural remains during the late stage of the last glacial. These remains represent characteristics of typical Late Paleolithic conditions in North China and distinctive early modern human behaviors, which place the Shuidonggou Loc2 occupants into the Homo sapiens sapiens population, not only from a time scale, but also from a cultural perspective. Prof. Gao Xing and his work team from the Institute of Vertebrate Paleontology and Paleoanthropology, CAS, published their recent achievement of addressing the conversion of subsistence patterns, as well as the mechanism of the Broad Spectrum Revolution through lithic technology, intelligence level and surviving strategy analysis of Shuidonggou Loc2 population. Shuidonggou site has been considered to be a typical Late Paleolithic site in North China, dozens of thousands of specimens, including stone artifacts, animal bones and ornaments were unearthed in cultural layer 1 and 2. This material also included eight earth-pit heaths. These specimens and relics provide reliable evidence for evaluating the property of Shuidonggou Loc2. Dr. Guan Ying, the first author of the article, who is also from Institute of Vertebrate Paleontology and Paleoanthropology, CAS made such statement “the conversion of subsistence patterns was generally accompanied with rapid diversification in hunting, food processing technologies, social group organization, and the invention of food storage equipment, etc. The gathering and processing of grass seeds in Shuidonggou Loc2 demonstrates that ancient occupants have already expanded their food resources during the 30-20 ka BP interval, and had shift gathering targets from low-energy consuming but high-energy returning objects to high-energy consuming and returning objects. We suggest that the BSR occurred in the SDG area during the SDG Loc2 occupational period, and subsequently affected wild plant exploitation patterns in adjacent area.” The original article was published in Volume 57 Issue 1 of the Chinese Science Bulletin in February of 2012.

Divergence of Duplicate Genes in Exon-intron Structure: Underlying Mechanisms and Importance in Organismal Evolution

Gene duplications are arguably the driving force of organismal evolution. Duplicate genes, if survived, tend to diverge in regulatory and coding regions. Coding divergences, which are usually prerequisite of functional differentiation, can be caused by nucleotide substitutions or exon-intron structural changes. Scientists have had limited knowledge in the latter case until recently, when Prof. Kong Hongzhi and his research group at the State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, CAS, investigated the prevalence, importance and underlying mechanisms of structural divergences during the evolution of duplicate and non-duplicate genes. They analyzed 612 pairs of paralogous genes and 300 pairs of orthologous genes in model plants and found that changes in exon-intron structure have been widespread in gene evolution. They also found that divergences in exon-intron structure can be accomplished through three main types of mutations (i.e. intra-exonic insertion/deletion, exonization/pseudoexonization, and exon/intron gain/loss), each of which contributed differently to structural divergence. Notably, however, compared with paralogs with similar evolutionary times, orthologs have accumulated significantly fewer structural changes, whereas the amounts of amino acid replacements remained largely unchanged. This suggests that structural divergences have played a more important role during the evolution of duplicate rather than non-duplicate genes and have led to the generation of genes with novel functions in short times. These findings help better understand the general patterns of gene evolution and highlighted the importance of structural divergence in gene and organismal evolution (PNAS, 2012, doi:10.1073/pnas.1109047109) .