Reference Assembly of Chromosome 7A as a Platform to Study Regions of Agronomic Importance

This presentation provides a report on the sequencing of wheat chromosome 7A.

The IWGSC programme established the capacity to prepare BAC libraries from flow sorted short and long arms of chromosome 7A (J. Dolezel et al., unpublished).  A total of 11,000 BACs were selected for inclusion into a minimum tiling path (MTP) for chromosome 7A (M. Luo, unpublished) based on restriction fragment analyses using the end-labelling SnapShot technology. The MTP consisted of 732 physical contigs, assembled using the LTC software (Z. Frenkel et al.). A total of 814 BAC pools with a maximum of 25 BACs represented the physical contigs for the first phase of sequencing with Illumina HiSeq.

A linear assembly of the physical contigs was produced using a high resolution molecular genetic map of 4,085 markers based on 1,000 segregating lines from an 8-way MAGIC cross (E. Huang, C. Cavanagh, M. Hayden, unpublished).  The 4,085 markers on chromosome 7A allowed over 90% of the 732 physical contigs to be anchored into a linear order and aligned to other maps with trait-association information.  The 7A reference genetic map is based on data from the CSxRenan map (P. Sourdille, B. Darrier, F. Choulet, E. Paux, unpublished), which provided the information for the chromosome 3B reference assembly, with the MAGIC map based markers providing a higher resolution in most regions of the chromosome. Mate-pair libraries (D. Konkin, A. Sharpe, C. Pozniak, unpublished) were used to improve the contiguity of the assembled sequence.

Known regions of 7A relating to grain quality and yield have been projected onto the chromosome assembly to provide sequence-level information for further study.