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Distinct classes of mitotic cyclins are differentially expressed in the soybean shoot apex during the cell cycle
1Department of Applied Physiology, National Institute of Agrobiological Resources, Ibaraki, Japan.
Abstract:
Protein phosphorylation by the complexes of cyclin and cyclin-dependent kinase plays a key role in cell cycle progression in all eukaryotes. The amplification by polymerase chain reaction of a cyclin box from developing root nodules and root apices of soybean showed the expression of a number of different molecular species of mitotic cyclins in plant meristems, and they were classified into five distinct groups based on their sequence similarities. The complete soybean cyclin cDNAs, cyc1Gm to cyc5Gm, corresponding to each group were isolated, and their predicted amino acid sequences showed clear similarities to mitotic cyclins identified from various organisms. These genes are expressed predominantly in such meristematic tissues as root and shoot apices and young developing nodules. Double-target in situ hybridization involving histone H4 as an S-phase marker allowed us to estimate the phases during which these cyclin genes are abundantly expressed. The results indicated that cyc5Gm is expressed in G2-to-M phases and cyc3Gm is expressed from late S-to-G2 phases. These expression patterns, together with the sequence criteria, strongly suggest that cyc3Gm and cyc5Gm encode the plant cognates for A- and B-type cyclins, respectively. In addition, the expression of cyc1Gm was restricted during a short period in S phase, suggesting that it belongs to a novel class of plant cyclins. Sequence comparison of 18 plant mitotic cyclins cloned thus far showed that they can be divided into four distinct structural groups with different functions in cell cycle progression.
Insights
Soybean mitotic cyclins were identified and classified into five groups. Specific cyclins like cyc5Gm and cyc3Gm show distinct cell cycle phase expression, suggesting roles akin to plant A- and B-type cyclins.
Area of Science:
- Plant molecular biology
- Cell cycle regulation
- Biochemistry
Background:
- Protein phosphorylation by cyclin-dependent kinase complexes is crucial for eukaryotic cell cycle progression.
- Mitotic cyclins regulate cell division in plants, but their diversity and specific roles remain incompletely understood.
Purpose of the Study:
- To identify and characterize novel soybean mitotic cyclins.
- To determine the cell cycle expression patterns of these soybean cyclins.
- To classify soybean cyclins based on sequence similarity and expression profiles.
Main Methods:
- Polymerase chain reaction (PCR) amplification of cyclin box sequences from soybean.
- Isolation and sequencing of complete soybean cyclin cDNAs (cyc1Gm to cyc5Gm).
- In situ hybridization using histone H4 as an S-phase marker to determine gene expression timing.
Main Results:
- Five distinct groups of soybean mitotic cyclins were identified, with cDNAs cyc1Gm to cyc5Gm isolated.
- These cyclins are predominantly expressed in meristematic tissues like root and shoot apices.
- cyc5Gm expression occurs in G2-to-M phases, cyc3Gm in late S-to-G2 phases, and cyc1Gm in S phase, suggesting roles as plant A- and B-type cyclin cognates and a novel cyclin class, respectively.
Conclusions:
- Soybean cyc3Gm and cyc5Gm likely function as plant cognates for A- and B-type cyclins, respectively.
- cyc1Gm represents a potentially novel class of plant cyclins with S-phase specific expression.
- Plant mitotic cyclins can be categorized into four structural groups with distinct cell cycle functions.