Arabidopsis replication factor C4 is critical for DNA replication during the mitotic cell cycle

Area of Science:

• Plant Molecular Biology
• Cell Cycle Regulation
• DNA Replication Mechanisms

Background:

• Replication Factor C (RFC) is a conserved eukaryotic complex vital for DNA replication and cell cycle progression.
• While RFC functions are known in yeast and fruit flies, their roles in higher plants, particularly RFC4, remain largely uncharacterized.
• Previous studies in Arabidopsis focused on AtRFC1 and AtRFC3, leaving the specific functions of other subunits like AtRFC4 unclear.

Purpose of the Study:

• To investigate the function of the Arabidopsis RFC4 (AtRFC4) gene in plant development.
• To determine the specific roles of AtRFC4 in DNA replication, embryo development, and cell cycle progression in plants.
• To elucidate the necessity of AtRFC4 expression in both embryo and endosperm for successful seed development.

Main Methods:

• Generated an Arabidopsis mutant with a loss-of-function mutation in AtRFC4 (rfc4-1).
• Analyzed the developmental phenotypes of the rfc4-1 mutant, including embryo and endosperm development.
• Performed complementation studies using embryo-specific (DD45pro, ABI3pro) and endosperm-specific (FIS2pro) promoters to express AtRFC4.
• Assessed DNA content and cell cycle progression (S-phase, M-phase) in mutant and complemented lines using flow cytometry.

Main Results:

• Loss of AtRFC4 function resulted in early sporophyte lethality, with embryos arresting at the two- to four-cell stage.
• Mutant embryos exhibited disrupted DNA replication and blocked mitosis in both embryo and endosperm.
• Complementation with embryo-specific or endosperm-specific promoters alone did not fully rescue the phenotype; combined expression was required for viable seed development.
• Analysis of root apical meristem cells revealed a decreased proportion of late S-phase and M-phase cells, indicating cell cycle arrest.

Conclusions:

• AtRFC4 is essential for DNA replication and cell cycle progression in Arabidopsis.
• Simultaneous function of AtRFC4 in both the embryo and endosperm is critical for successful seed development.
• Endosperm proliferation, dependent on AtRFC4, is crucial for embryo maturation.
• Disrupted DNA replication due to AtRFC4 deficiency triggers cell cycle arrest, highlighting its fundamental role in plant development.