The Cucurbita maxima ribosomal DNA intergenic spacer has a complex structure.

Area of Science:

• Molecular Biology
• Genetics
• Plant Science

Background:

• Ribosomal DNA (rDNA) contains coding regions and intergenic spacers (IGS).
• The IGS plays a role in rDNA gene regulation and evolution.
• Understanding IGS structure is crucial for plant genetics.

Purpose of the Study:

• To determine the nucleotide sequence of the intergenic spacer (IGS) in Cucurbita maxima rDNA.
• To analyze the complex primary structure and repetitive elements within the C. maxima IGS.
• To compare the C. maxima IGS with other plant IGS sequences for evolutionary insights.

Main Methods:

• DNA sequencing of the intergenic spacer (IGS) region of Cucurbita maxima rDNA.
• Bioinformatic analysis to identify repetitive families and unique domains.
• Comparative analysis of nucleotide sequences and restriction maps with related plant species (C. pepo, C. sativa).

Main Results:

• The sequenced fragment is 6142 nt long, including the 5508-nt IGS.
• The C. maxima IGS exhibits a complex structure with five repetitive families (A-E) and three unique domains.
• The IGS is dominated by tandem repeats, including nine units of ~250 nt (repeat D) and a G+C rich region with ~42 nt repeats (repeat C).
• The 5' portion of the cucurbit IGS shows higher evolutionary conservation compared to other regions.

Conclusions:

• The intergenic spacer (IGS) of Cucurbita maxima rDNA is exceptionally long and structurally complex compared to other known plant IGSs.
• Sequence variability, including nucleotide changes, insertions, and deletions, is present within the repetitive units.
• Comparative analyses suggest that the 5' region of the cucurbit IGS is more conserved evolutionarily.