SCAR (sequence characterized amplified region) markers allow the reliable identification of unique
somaclonal variations. Six SCAR markers were developed previously and were thought to be exclusively
characteristic of eight maize somaclones. However, we detected two of these markers in maize lines and
a cultivar unrelated to the progenitor line of the somaclones. Therefore, we sequenced these markers and
performed bioinformatic searches to understand the molecular events that may underlie the variability
observed in the somaclones. All changes were found in noncoding sequences and were induced by different
molecular events, such as the insertion of long terminal repeat (LTR) transposon(s), precise miniature
inverted repeat transposable element (MITE) excision, microdeletion, recombination, and a change in the
pool of mitochondrial DNA. For example, the SCAR marker QR is represented by the two variants QR-A
and QR-2. The sequences of the two variants were similar, except for a 457-bp fragment found only in
QR-A; this region was denoted as Q. Region Q was flanked by the direct 3-bp repeat 5-TAA-3 (target site
duplication; TSD) and the inverted 14-bp repeat 5-GGGCCTGTTTGGAA-3 (terminal inverted repeats;
TIRs). These features confer the Q region with similarity to the nonautonomic Tourist-like MITE. In two
groups of independently produced somaclones, the same features (morphological, molecular) were variable,
which confirms the theory of ‘hot spots’ occurring in the genome. The distribution of one of the
SCAR markers was confirmed using Southern blot hybridization. The presence of the same molecular
markers in the somaclones and in different non-somaclonal maize variants suggests that in some cases,
the same mechanisms determine both in vitro and in vivo variability and that cell culture enhances the
rate of heritable genomic changes that naturally occur in living organisms