Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2007
Publication Date: 9/1/2007
Citation: Ipek, M., Ipek, A., Senalik, D.A., Simon, P.W. 2007. Characterization of an Unusual Cytoplasmic Chimera Detected in Bolting Garlic (Allium sativum L.) Clones. Journal of the American Society for Horticultural Science. 132:664-669. Interpretive Summary: Garlic is an economically important horticultural crop known from antiquity. Of all the varying attributes of garlic, flowering or "bolting" habit has been the primary character used to categorize garlic clones by consumers, horticulturists and botanists. Non-bolting garlic clones are commonly grown around the world and they usually yield more than bolting clones. While bolting is a very important character, there is no rapid test for bolting, and the crop must be grown for nearly a year to evaluate this important trait. In earlier studies we observed molecular (DNA) markers that might accurately and rapidly predict whether a given garlic plant will bolt or not. In this study, we describe an unusual molecular marker to discriminate bolting garlic from non-bolting. This research is of interest to garlic growers, to crop science and molecular biology researchers.
Technical Abstract: Production of a visible flower stalk or bolting has been used as a major trait to categorize garlic clones. Analysis of mitochondrial genome variation with PCR revealed differences between bolting and non-bolting clones of garlic. Screening 333 garlic accessions from diverse geographic origins revealed a 1,403 bp mitochondrial DNA marker associated with bolting that we call BltM. BltM did not amplify in any of the 131 non-bolting clones, while amplification of this marker was observed in 127 of 130 (97.7%) garlic clones that bolted completely in Wisconsin. Seventy-two garlic clones bolted incompletely (clones in which some but not all of the plants bolted) and this marker was not amplified in 69 (95.8%) of these clones. Due to the significant association of BltM with bolting, this PCR based marker can be used to reliably discriminate completely bolting garlic clones from non-bolting and incomplete bolting ones. Sequence characterization of this marker revealed that BltM is a chimera involving both mitochondrial and chloroplast DNA. The DNA sequences including and flanking both the 5’ and 3’ ends of this marker are consistent with an approximately 4.8 kbp chloroplast DNA fragment having been inserted into the mitochondrial genome downstream from the mitochondrial cox3 gene. Sequence alignment of the chloroplast genes in this chimeric region with the homologous sequences in GenBank indicate the presence of deletions, insertions, and single nucleotide polymorphisms in the coding sequences, resulting in putative incomplete open reading frames or frame shift mutations. Hence, we speculate that this insertion may have occurred long ago in the evolution of garlic.