Tobacco mitotic cyclins: cloning, characterization, gene expression and functional assay

Area of Science:

• Molecular Biology
• Plant Science
• Cell Biology

Background:

• Cyclins are key regulators of the cell cycle, controlling progression through different phases.
• Understanding plant cyclins is crucial for comprehending cell division and growth in plants.

Purpose of the Study:

• To isolate and characterize novel tobacco cyclins.
• To determine the cell cycle phase-specific expression patterns of these cyclins.
• To investigate the functional roles of these cyclins in cell cycle progression.

Main Methods:

• Polymerase Chain Reaction (PCR) cloning was used to isolate cyclin cDNA clones from tobacco (Nicotiana tabacum).
• Expression analysis was performed on synchronized tobacco suspension cultured cells to determine mRNA levels across cell cycle phases (S, G2, M).
• Functional complementation assays were conducted using Saccharomyces cerevisiae G1 cyclin mutants.

Main Results:

• Three cyclin cDNA clones, designated Ntcyc25, Ntcyc27, and Ntcyc29, were successfully isolated.
• Ntcyc25 and Ntcyc27 were classified as A-type cyclins, with mRNA detectable from S to M phase.
• Ntcyc29 was classified as a B-type cyclin, with mRNA detected from G2 to M phase.
• Expression of all three cyclin genes correlated with active cell growth and ceased in the stationary phase.
• Ntcyc25 and Ntcyc29 (N-terminal truncated) could rescue yeast G1 cyclin mutants, and Ntcyc27 (full-length) partially performed G1 cyclin functions.

Conclusions:

• The identified tobacco cyclins (Ntcyc25, Ntcyc27, Ntcyc29) are homologous to known mitotic cyclins.
• Their distinct expression patterns support their classification as A-type and B-type cyclins, regulating specific cell cycle phases in tobacco.
• These cyclins play roles in cell growth and can functionally complement yeast cell cycle mutants, suggesting conserved roles in cell cycle control.