Multiple Divergent ITS1 Copies Were Identified in Single Tomato Genome Using DGGE Analysis
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The intra-genomic variation in the internal transcribed spacer (ITS) region has led to misleading conclusions in the evolutionary analysis of plants; understanding this variation is critical for correct evolutionary analysis based on ITS sequences. To reveal the ITS variation in tomato, entire copies of ITS1 sequences within tomato species were separated using denaturing gradient gel electrophoresis (DGGE) and DNA sequence analysis. ITS1 copies varied significantly in sequence composition, but not in sequence length within the same tomato cultivar. DNA sequence similarity of the ITS1 copies was 77–100 %. Moreover, AT and GC contents in ITS1 copies from each tomato cultivar were significantly different, ranging from 50.4 to 64.3 % for GC and from 35.7 to 49.6 % for AT. However, the length variation of ITS1 was insignificant, ranging from 279 to 282 bp. Multiple copies of divergent ITS1 present in the tomato genome indicate that some copies may be paralogues. In conclusion, DGGE technique is a reliable and novel approach to reveal the entire ITS copy variation and the possible evolutionary relationship of tomato.
KeywordsDivergent ITS copy DGGE GC content Solanum Tomato
This research was supported in part by grants from the USDA Sustainable Agriculture Research and Education (SARE) Program and in part by the North Carolina State University Agricultural Research Service. We would like to express our appreciation to Jinping Sun and Cary Rivard for their technical assistance and Stella Chang for editing the early version of the manuscript. We also would like to thank Dr. Bruce Baldwin for his suggestion through e-mail communication.
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