Abstract
BackgroundThe safety of genetically transformed plants remains a subject of scrutiny. Genomic variants in PRSV resistant transgenic papaya will provide evidence to rationally address such concerns.ResultsIn this study, a total of more than 74 million Illumina reads for progenitor ‘Sunset’ were mapped onto transgenic papaya ‘SunUp’ reference genome. 310,364 single nucleotide polymorphisms (SNPs) and 34,071 small Inserts/deletions (InDels) were detected between ‘Sunset’ and ‘SunUp’. Those variations have an uneven distribution across nine chromosomes in papaya. Only 0.27% of mutations were predicted to be high-impact mutations. ATP-related categories were highly enriched among these high-impact genes. The SNP mutation rate was about 8.4 × 10− 4 per site, comparable with the rate induced by spontaneous mutation over numerous generations. The transition-to-transversion ratio was 1.439 and the predominant mutations were C/G to T/A transitions. A total of 3430 nuclear plastid DNA (NUPT) and 2764 nuclear mitochondrial DNA (NUMT) junction sites have been found in ‘SunUp’, which is proportionally higher than the predicted total NUPT and NUMT junction sites in ‘Sunset’ (3346 and 2745, respectively). Among all nuclear organelle DNA (norgDNA) junction sites, 96% of junction sites were shared by ‘SunUp’ and ‘Sunset’. The average identity between ‘SunUp’ specific norgDNA and corresponding organelle genomes was higher than that of norgDNA shared by ‘SunUp’ and ‘Sunset’. Six ‘SunUp’ organelle-like borders of transgenic insertions were nearly identical to corresponding sequences in organelle genomes (98.18 ~ 100%). None of the paired-end spans of mapped ‘Sunset’ reads were elongated by any ‘SunUp’ transformation plasmid derived inserts. Significant amounts of DNA were transferred from organelles to the nuclear genome during bombardment, including the six flanking sequences of the three transgenic insertions.ConclusionsComparative whole-genome analyses between ‘SunUp’ and ‘Sunset’ provide a reliable estimate of genome-wide variations and evidence of organelle-to-nucleus transfer of DNA associated with biolistic transformation.
Highlights
The safety of genetically transformed plants remains a subject of scrutiny
Detected variations were randomly distributed amongst papaya chromosomes, whereas only 0.27% were predicted to have a disruptive impact on the protein function
Development of single nucleotide polymorphisms (SNPs)/InDel markers that occurred in high-impact genes could facilitate markerassisted Papaya Ringspot Virus (PRSV) disease resistance breeding in papaya
Summary
The safety of genetically transformed plants remains a subject of scrutiny. Genomic variants in PRSV resistant transgenic papaya will provide evidence to rationally address such concerns. Papaya (Carica papaya L.) is a diploid plant with a relatively small genome (2n = 18, 372 Mb) in the family Caricaceae [1]. It is one of the most popular tropical fruits owing to its exceptional nutritional and medicinal properties. In addition to the effects induced by transgene copy numbers and integration sites, other factors such as somaclonal variations during tissue culture and spontaneous mutations during meiosis of over 25 generations might induce segregated genomic variants, which would lead to the divergence of phenotypic and functional features between ‘Sunset’ and ‘SunUp’
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