Biology subjects

King, G.

Publications and source records attributed to King, G..

4 recordsLinked to original sources

bioRxiv2018

Genome-wide selection footprints and deleterious variations in young Asian allotetraploid rapeseed

Brassica napus (AACC, 2n=38), is an important oilseed crop grown worldwide. However, little is known about the population evolution of this species, the genomic difference between its major genetic clusters, such as European and Asian rapeseed, and impacts of historical large-sale introgression events in this young tetraploid. In this study, we reported the de novo assembly of the genome sequences of an Asian rapeseed (B. napus), Ningyou 7 and its four progenitors and carried out de novo assembly-based comparison, pedigree and population analysis with other available genomic data from diverse European and Asian cultivars. Our results showed that Asian rapeseed originally derived from European rapeseed, but it had subsequently significantly diverged, with rapid genome differentiation after intensive local breeding selection. The first historical introgression of B. rapa dramatically broadened the allelic pool of Asian B. napus, but decreased their deleterious variations. The secondary historical introgression of European rapeseed (canola-quality) has reshaped Asian rapeseed into two groups, accompanied by an increase in genetic load. This study demonstrates distinctive genomic footprints by recent intra- and inter-species introgression events for local adaptation, and provide novel insights for understanding the rapid genome evolution of a young allopolyploid crop.

genomics↗

bioRxiv2018

The atypical thiol-disulfide exchange protein α-DsbA2 from Wolbachia pipientis is a homotrimeric disulfide isomerase

DiSulfide Bond (DSB) oxidative folding enzymes are master regulators of virulence localized to the periplasm of many Gram-negative bacteria. The archetypal DSB machinery from Escherichia coli K12 has a dithiol oxidizing redox relay pair (DsbA/B), a disulfide isomerizing redox relay pair (DsbC/D) and specialist reducing enzymes DsbE and DsbG that also interact with DsbD. By contrast the Gram-negative bacterium Wolbachia pipientis encodes just three DSB enzymes. Two of these -DsbA1 and -DsbB form a redox relay pair analogous to E. coli DsbA/B. The third enzyme -DsbA2 incorporates a DsbA-like sequence but does not interact with -DsbB. In comparison with other DsbA enzymes, -DsbA2 has [~]50 extra N-terminal residues. The crystal structure of -DsbA2{Delta}N, the N-terminally truncated form in which these residues are removed confirms the DsbA-like nature of this domain. However, -DsbA2 does not have DsbA-like activity: it is structurally and functionally different as a consequence of its N-terminal residues. First, -DsbA2 is a powerful disulfide isomerase and a poor dithiol oxidase - ie its role is to shuffle rather than introduce disulfide bonds. Moreover, small-angle X-ray scattering of -DsbA2 reveals a homotrimeric arrangement. Our results allow us to draw conclusions about the factors required for functionally equivalent enzymatic activity across structurally diverse protein architectures.

biochemistry↗

bioRxiv2018

Glycosyltransferase homologs prevent promiscuous cell aggregation and promote multicellular development in the choanoflagellate S. rosetta

The mechanisms underlying multicellular development in the animal stem lineage may be reconstructed through the study of choanoflagellates, the closest living relatives of animals. To determine the genetic underpinnings of multicellularity in the emerging model choanoflagellate S. rosetta, we performed a screen for mutants with defects in multicellular rosette development. In two of the mutants, Jumble and Couscous, single cells failed to develop into orderly rosettes but instead aggregated promiscuously into amorphous clumps of cells. Both mutants mapped to lesions in genes encoding glycosyltransferases and the mutations perturbed glycosylation patterns in the extracellular matrix (ECM). In animals, glycosyltransferases transfer activated sugars to donor molecules and thereby sculpt the polysaccharide-rich ECM, regulate integrin and cadherin activity, and, when disrupted, contribute to tumorigenesis. The finding that glycosyltransferases promote proper rosette development and prevent cell aggregation in S. rosetta suggests a pre-metazoan role for glycosyltransferases in regulating development and preventing abnormal tumor-like multicellularity.\n\nIMPACT STATEMENTA genetic screen reveals that glycosyltransferases are required for proper rosette development and the prevention of cell clumping in one of the closest living relatives of animals, the choanoflagellate S. rosetta.

genetics↗

bioRxiv2017

Pivotal roles of PCNA loading and unloading on heterochromatin function

In Saccharomyces cerevisiae, heterochromatin structures required for transcriptional silencing of the HML and HMR loci are duplicated in coordination with passing DNA replication forks. Despite major reorganization of chromatin structure, the heterochromatic, transcriptionally-silent states of HML and HMR are successfully maintained throughout S-phase. Mutations of specific components of the replisome diminish the capacity to maintain silencing of HML and HMR through replication. Similarly, mutations in histone chaperones involved in replication-coupled nucleosome assembly reduce gene silencing. Bridging these observations, we determined that the PCNA unloading activity of Elg1 was important for coordinating DNA replication forks with the process of replication-coupled nucleosome assembly to maintain silencing of HML and HMR through S-phase. Collectively these data identified a mechanism by which chromatin reassembly is coordinated with DNA replication to maintain silencing through S-phase.\n\nSIGNIFICANCE STATEMENTDNA replication poses a unique logistical challenge for the cell in that structural features of chromatin and their regulatory functions must be carefully coordinated with passage of replication machinery so faithful duplication of both the genome and its chromatin structures may be achieved. Nucleosome assembly is fundamental to reestablishment of chromatin in the wake of DNA replication, and here a mechanism by which nucleosome assembly is coordinated with DNA replication to maintain silenced chromatin is described.

genetics↗