Oxford Nanopore MinION Sequencing and Genome Assembly

The revolution of genome sequencing is continuing after the successful secondgeneration sequencing （SGS） technology. The third-generation sequencing （TGS） technology, led by Pacific Biosciences （PacBio）, is progressing rapidly, moving from a technology once only capable of providing data for small genome analysis, or for performing targeted screening, to one that promises high quality de novo assembly and structural variation detection for human-sized genomes. In 2014, the MinION, the first commercial sequencer using nanopore technology, was released by Oxford Nanopore Technologies （ONT）. MiniON identifies DNA bases by measuring the changes in electrical conductivity generated as DNA strands pass through a biological pore. Its portability, affordability, and speed in data production makes it suitable for real-time applications, the release of the long read sequencer MiniON has thus generated much excitement and interest in the genomics community. While de novo genome assemblies can be cheaply produced from SGS data, assem- bly continuity is often relatively poor, due to the limited ability of short reads to handle long repeats. Assembly quality can be greatly improved by using TGS long reads, since repetitive regions can be easily expanded into using longer sequencing lengths, despite having higher error rates at the base level. The potential of nanopore sequencing has been demonstrated by various studies in genome surveillance at locations where rapid and reliable sequencing is needed, but where resources are limited.

Cytoplasmic and nuclear genome variations of rice hybrids and their parents inform the trajectory and strategy of hybrid rice breeding

The male sterility(MS)line is a prerequisite for efficient production of hybrid seeds in rice,a self-pollinating species.MS line breeding is pivotal for hybrid rice improvement.Understanding the historical breeding tra-jectory will help to improve hybrid rice breeding strategies.Maternally inherited cytoplasm is an appro-priate tool for phylogenetic reconstruction and pedigree tracing in rice hybrids.In this study,we analyzed the cytoplasmic genomes of 1495 elite hybrid rice varieties and identified five major types of cytoplasm,which correspond to different hybrid production systems.As the cytoplasm donors for hybrids,461 MS lines were also divided into five major types based on cytoplasmic and nuclear genomic architecture.Spe-cific core accessions cooperating with different fertility-associated genes drove the sequence divergence of MS lines.Dozens to hundreds of convergent and divergent selective sweeps spanning several agro-nomic trait-associated genes were identified among different types of MS lines.We further analyzed the cross patterns between different types of MS lines and their corresponding restorers.This study system-atically analyzed the cytoplasmic genomes of rice hybrids revealed their relationships with nuclear ge-nomes of MS lines,and illustrated the trajectory of hybrid rice breeding and the strategies for breeding different types of MS lines providing new insights for future improvement of hybrid rice.