PCR-mediated recombination in amplification products derived from polyploid cotton

PCR recombination describes a process of in vitro chimera formation from non-identical templates. The key requirement of this process is the inclusion of two partially homologous templates in one reaction, a condition met when amplifying any locus from polyploid organisms and members of multigene families from diploid organisms. Because polyploids possess two or more divergent genomes ("homoeologues") in a common nucleus, intergenic chimeras can form during the PCR amplification of any gene. Here we report a high frequency of PCR-induced recombination for four low-copy genes from allotetraploid cotton (Gossypium hirsutum). Amplification products from these genes (Myb3, Myb5, G1262 and C(es)A1) range in length from 860 to 4,050 bp. Intergenomic recombinants were formed frequently, accounting for 23 of the 74 (31.1%) amplicons evaluated, with the frequency of recombination in individual reactions ranging from 0% to approximately 89%. Inspection of the putative recombination zones failed to reveal sequence-specific attributes that promote recombination. The high levels of observed in vitro recombination indicate that the tacit assumption of exclusive amplification of target templates may often be violated, particularly from polyploid genomes. This conclusion has profound implications for population and evolutionary genetic studies, where unrecognized artifactually recombinant molecules may bias results or alter interpretations.