Central Idea

• Organisms on Earth are categorized into prokaryotes and eukaryotes, with distinct characteristics and evolutionary lineages.
• Archaea, a subset of unicellular organisms, were discovered to have a different lineage than bacteria and are found in extreme environments.
• Some archaea, known as the Asgard, exhibit similarities to eukaryotes, leading to insights into the origins of mitochondria and the evolution of complex life forms.

This article explores the endosymbiotic relationships between archaea and bacteria, the origins of mitochondria, and the unique evolutionary paths taken by plants.

Archaea and Unique Lineages

• Prokaryotes and Eukaryotes: Organisms are broadly divided into prokaryotes (unicellular, lacking organelles and nucleus) and eukaryotes (contain organelles and nucleus, often complex and multicellular).
• Archaea’s Distinct Lineage: Archaea differ from bacteria in cell wall composition and gene sequence and were initially found in extreme environments.
• Asgard Archaea: Asgard archaea, named after Norse mythology, exhibit proteins resembling eukaryotic proteins and are found in unique ecosystems.

Origins of Mitochondria and Chloroplasts

• Endosymbiotic Theory: Mitochondria and chloroplasts, responsible for energy generation and photosynthesis, respectively, evolved from free-living bacteria through endosymbiosis.
• Mitochondria’s Origin: Mitochondria evolved from a proteobacteria that was engulfed by an Asgard archaea, leading to the development of animals, fungi, and plants.
• Plant Evolution: In plants, the Asgard-mitochondrial union was followed by the incorporation of a photosynthesizing cyanobacterium, which became the chloroplast.

Complexity of such Relationships

• Challenges of Symbiosis: Establishing a functional symbiotic relationship between independent life forms presents challenges.
• Plant Approach: Plants made choices to optimize gene retention, favoring archaean genes for information technology processes and bacterial genes for operations and housekeeping tasks.
• Gene Transfer to the Nucleus: Over time, many mitochondrial genes were transferred to the nucleus, creating a more efficient arrangement.

Insights from Cellular Process Studies

• Reconfiguring Cellular Processes: The research of Rajan Sankaranarayanan’s group at CCMB focuses on understanding the reconfiguration of cellular processes in endosymbiotic relationships.
• Animal and Fungal Adaptations: Animals and fungi adapt by inducing changes in mitochondria to work around discrepancies in amino acid discrimination mechanisms.
• Plant Evolution Complexity: Plants handle the complexity of three gene sets involved in their evolution by segregating policing machineries in the cytoplasm and mitochondria.

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