June 1, 2021  |  

Direct sequencing and identification of damaged DNA bases.

DNA is under constant stress from both endogenous and exogenous sources. DNA base modifications resulting from various types of DNA damage are wide-spread and play important roles in affecting physiological states and disease phenotypes. Examples include oxidative damage (8- oxoguanine, 8-oxoadenine; aging, Alzheimer’s, Parkinson’s), alkylation (1-methyladenine, 6-O- methylguanine; cancer), adduct formation (benzo[a]pyrene diol epoxide (BPDE), pyrimidine dimers; smoking, industrial chemical exposure, chemical UV light exposure, cancer), and ionizing radiation damage (5-hydroxycytosine, 5- hydroxyuracil, 5-hydroxymethyluracil; cancer). Currently, these and other products of DNA damage cannot be sequenced with existing sequencing methods. In contrast, single molecule, real-time (SMRT) DNA sequencing can report on modified DNA bases through an analysis of the DNA polymerase kinetics that is affected by a modified base in the template. We demonstrate the DNA strand-resolved sequencing of over 8 different DNA-damage associated base modifications, with base pair resolution and single DNA molecule sensitivity. We also report on the application of this sequencing capability to biological samples and the development of a generic, open-source algorithm to analyze kinetic information from SMRT sequencing.

April 21, 2020  |  

Complete genome sequence of Pseudomonas frederiksbergensis ERDD5:01 revealed genetic bases for survivability at high altitude ecosystem and bioprospection potential.

Pseudomonas frederiksbergensis ERDD5:01 is a psychrotrophic bacteria isolated from the glacial stream flowing from East Rathong glacier in Sikkim Himalaya. The strain showed survivability at high altitude stress conditions like freezing, frequent freeze-thaw cycles, and UV-C radiations. The complete genome of 5,746,824?bp circular chromosome and a plasmid of 371,027?bp was sequenced to understand the genetic basis of its survival strategy. Multiple copies of cold-associated genes encoding cold active chaperons, general stress response, osmotic stress, oxidative stress, membrane/cell wall alteration, carbon storage/starvation and, DNA repair mechanisms supported its survivability at extreme cold and radiations corroborating with the bacterial physiological findings. The molecular cold adaptation analysis in comparison with the genome of 15 mesophilic Pseudomonas species revealed functional insight into the strategies of cold adaptation. The genomic data also revealed the presence of industrially important enzymes.Copyright © 2018 Elsevier Inc. All rights reserved.

April 21, 2020  |  

Comprehensive characterization of T-DNA integration induced chromosomal rearrangement in a birch T-DNA mutant.

Integration of T-DNA into plant genomes via Agrobacterium may interrupt gene structure and generate numerous mutants. The T-DNA caused mutants are valuable materials for understanding T-DNA integration model in plant research. T-DNA integration in plants is complex and still largely unknown. In this work, we reported that multiple T-DNA fragments caused chromosomal translocation and deletion in a birch (Betula platyphylla × B. pendula) T-DNA mutant yl.We performed PacBio genome resequencing for yl and the result revealed that two ends of a T-DNA can be integrated into plant genome independently because the two ends can be linked to different chromosomes and cause chromosomal translocation. We also found that these T-DNA were connected into tandem fragment regardless of direction before integrating into plant genome. In addition, the integration of T-DNA in yl genome also caused several chromosomal fragments deletion. We then summarized three cases for T-DNA integration model in the yl genome. (1) A T-DNA fragment is linked to the two ends of a double-stranded break (DSB); (2) Only one end of a T-DNA fragment is linked to a DSB; (3) A T-DNA fragment is linked to the ends of different DSBs. All the observations in the yl genome supported the DSB repair model.In this study, we showed a comprehensive genome analysis of a T-DNA mutant and provide a new insight into T-DNA integration in plants. These findings would be helpful for the analysis of T-DNA mutants with special phenotypes.

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