Two functional soybean genes encoding p34cdc2 protein kinases are regulated by different plant developmental pathways

Area of Science:

• Plant Molecular Biology
• Cell Cycle Regulation
• Legume Biology

Background:

• The p34cdc2 protein kinase is a key regulator of the cell cycle in eukaryotes.
• Homologs of yeast cdc2/CDC28 genes are essential for cell division in various organisms.
• Soybean root nodules are a model system for studying plant-microbe interactions and organogenesis.

Purpose of the Study:

• To isolate and characterize soybean homologs of the yeast cdc2/CDC28 genes.
• To investigate the differential expression and function of these soybean p34cdc2 genes.
• To explore the role of p34cdc2 protein kinases in soybean nodule development and phytohormone signaling.

Main Methods:

• Isolation of cDNA clones (cdc2-S5 and cdc2-S6) from a soybean nodule cDNA library.
• Sequence analysis to determine homology and identify distinct noncoding regions.
• Functional complementation of yeast cdc28 mutation using soybean cDNA clones.
• Genomic Southern analysis to assess gene copy number and allelism.
• Quantitative analysis of gene expression in different soybean tissues and after Rhizobium infection.

Main Results:

• Two soybean cDNA clones, cdc2-S5 and cdc2-S6, encoding p34cdc2 protein kinases were identified, sharing high homology in coding regions but distinct noncoding sequences.
• Both soybean genes could rescue the yeast cdc28 mutation, albeit with varying efficiencies.
• Genomic Southern analysis revealed two unlinked, nonallelic copies for each gene.
• Differential expression was observed: cdc2-S5 is upregulated in roots and nodules, while cdc2-S6 is more abundant in aerial tissues.
• cdc2-S5 expression increased after Rhizobium infection and responded to auxin, suggesting a role in nodule initiation and organogenesis, while cdc2-S6 did not show these responses.

Conclusions:

• Soybean possesses at least two distinct genes encoding p34cdc2 protein kinases, with differential regulation tied to plant development.
• The soybean p34cdc2 gene, cdc2-S5, plays a significant role in root nodule development, potentially mediated by phytohormone signaling pathways activated during Rhizobium infection.
• These findings suggest that different p34cdc2 protein kinases may control cell division in specific plant tissues and respond to distinct environmental or developmental signals.