Methods for characterizing a target DNA sequence composition in a plant genome
Methods for the high-throughput analysis of transgenic events are herein disclosed. The methods use libraries of sheared genomic DNA ligated to specialized adapters and pooled for sequence analysis and comparison to known genomic and insert sequence. The method finds use in detecting characterizing insertion site, transgene integrity, and transgene copy number.
1. A method for characterizing a target sequence in the genome of a plant, the method comprising:
a) isolating and purifying a sample of genomic DNA;
b) shearing the genomic DNA into fragments to create a library;
c) ligating the library fragments to adapter sequences having barcodes;
d) designing construct-specific PCR primers wherein one primer targets insert sequence and a second PCR primer targets the adapter; wherein the primers are designed for every 200 base pairs on alternating stands, or for every 400 base pairs on a single strand;
e) amplifying the DNA using the PCR primers of d), thereby enriching the library for DNA sequences;
f) pooling the enriched library in equal molar ratios into sample pools;
g) sequencing the sample pools to obtain reads;
h) filtering and aligning the reads to the genomic sequence of a control plant and to the target sequence of interest;
i) selecting reads that align to the target sequence of interest;
j) determining junction sequences from the selected reads; and
k) using the junction sequences to characterize the integrity of the target sequence of interest in the genome of the sample plant.
2. The method of claim 1 wherein the sheared genomic DNA fragments range from about 50 base pairs in length to about 2.5 kb in length.
3. The method of claim 1 wherein the sheared genomic DNA fragments range from about 200 base pairs in length to about 1 kb in length.
4. The method of claim 1 wherein the sheared genomic DNA fragments are about 400 base pairs in length.
5. The method of claim 1 wherein the PCR primers are nested.
6. The method of claim 1 wherein the PCR primers are overlapping.
7. The method of claim 1 wherein the enriched library is analyzed for PCR artifacts.
8. The method of claim 1 , wherein the reads obtained in step (g) are processed to remove any adapter sequence information.
9. The method of claim 1 , wherein sequencing in step (g) produces at least 1 million reads.
10. The method of claim 1 , wherein the reads are 100 bp paired-end reads.
11. The method of claim 1 , wherein the top 60% most abundant reads obtained from step (g) are selected for alignment to the genomic sequence of a control plant and to the target sequence of interest.
12. The method of claim 1 , wherein determining the junction sequences in step (j) comprises aligning at least two reads corresponding to a junction sequence and identifying a consensus junction sequence.
13. The method of claim 12 , wherein the consensus junction sequence comprises:
about 30 nucleotides aligning to the genome sequence of the control plant, and about 20 nucleotides aligning to the target sequence of interest.
14. The method of claim 1 , wherein the ends of the junction sequence are extended to provide a junction contig of about 100 to about 3000 nucleotides.
15. The method of claim 14 , wherein the ends of the junction sequence are extended by aligning overlapping reads at each end of the junction sequence in order to identify the nucleotide sequence flanking each end of the junction sequence.
16. The method of claim 12 , wherein the ends of the junction sequence are extended using SSAKE.
17. The method of claim 1 , wherein the ends of the junction sequence are aligned to the genomic sequence of a control plant and to the target sequence of interest.
18. The method of claim 1 , wherein step (h) further comprises excluding endogenous reads from further analysis.
19. The method of claim 1 , the method further comprising selecting a sample plant for advancement based on the number, location, integrity, or any combination thereof, of the target sequence of interest in the genome of the sample plant.
20. The method of claim 19 , further comprising using the selected sample plant in a plant breeding program, wherein a use in the breeding program comprises introgressing a gene of interest in the selected sample plant into another plant, crossing the selected sample plant, pedigree breeding with the selected sample plant, using the selected sample plant recurrent selection, using the selected sample plant in mass selection, or mutation breeding with the selected sample plant.
21. A method for characterizing a target sequence in the genome of a plant, the method comprising:
a) sequencing sample pools comprising an enriched library to obtain reads, wherein the enriched library comprises plant genomic DNA, wherein the plant genomic DNA has a target sequence of interest;
b) filtering and aligning the reads to the genomic sequence of a control plant and to the target sequence of interest;
c) selecting reads that align to the target sequence of interest;
d) determining junction sequences from the selected reads; and
e) using the junction sequences to characterize the integrity of the target sequence of interest in the genome of the sample plant.
22. The method of claim 21 , wherein the sample pools comprise more than one enriched library.
23. The method of claim 1 , further comprising characterizing the integrity of the target sequence of interest by analyzing read alignments to the target sequence to identify insertions, deletions, or rearrangements of the target sequence of interest.
24. The method of claim 21 , further comprising characterizing the integrity of the target sequence of interest by analyzing read alignments to the target sequence to identify insertions, deletions, or rearrangements of the target sequence of interest.