The single-cell transcriptome program of nodule development cellular lineages in Medicago truncatula.

Area of Science:

• Plant Biology
• Microbiology
• Genetics

Background:

• Legumes form symbiotic relationships with nitrogen-fixing rhizobia, developing root nodules.
• Cellular development in nodules is a response to bacterial infection, but transcriptional changes are poorly understood.

Purpose of the Study:

• To characterize cell-type-specific transcriptional responses in Medicago truncatula roots during early nodule development.
• To identify new regulators of nodulation using wild-type and hypernodulating mutant genotypes.

Main Methods:

• Single-cell RNA sequencing of Medicago truncatula roots during rhizobia symbiosis.
• Analysis of wild-type (Jemalong A17) and hypernodulating (sunn-4) mutant transcriptomes.
• Gene regulatory network analysis and functional validation of identified regulators.

Main Results:

• Identified epidermal root hair and stele cell types responding to rhizobia infection.
• Showed cortex-derived cell lineages differentiate into nodule primordia and meristems.
• Identified novel nodulation regulators, including STYLISH 4, and validated its function.

Conclusions:

• Transcriptional reprogramming in root cells is crucial for legume-rhizobia symbiosis.
• Specific cell types and gene regulatory networks govern nodule development and proliferation.
• STYLISH 4 is a newly identified regulator of legume nodulation.