
Like animals, plant life originated in the sea and only colonized land once they evolved the necessary adaptations. For animals, this meant developing mechanisms for breathing air and terrestrial locomotion. For plants, the primary challenge was desiccation, creating strong selection pressure for traits that mitigated water loss. This led to the evolution of a highly connected network of genes, known as a 'hub,' that regulates responses to environmental stress.
So fundamental is this genetic hub to plant survival that it has remained highly conserved throughout evolutionary history.
What information do you have on the evidence for the evolution of land plants and their divergence from marine algae?Now a team of researchers from Georg-August-Universität, Göttingen, Germany, led by Professor Jan de Vries, Göttingen University, who led the research, explains: has shown that this same 'hub' is present in both mosses and algae, even though they diverged 600 million years ago, the mosses having evolved out of simple algae.The evolution of land plants from their algal ancestors is one of the most significant transitions in Earth's history. Multiple lines of evidence, including molecular phylogenetics, comparative genomics, palaeobotany, and developmental biology, support the hypothesis that land plants (embryophytes) evolved from a group of green algae, specifically within the Charophyte clade. Below is a summary of the key evidence:Conclusion
- Molecular and Phylogenetic Evidence
- Shared Genetic Markers: Molecular phylogenetic studies show that land plants are most closely related to charophyte algae, such as Chara and Klebsormidium.
- Chloroplast DNA Similarities: Land plants and charophytes share specific gene arrangements in their chloroplast DNA, supporting common ancestry.
- Cellulose Synthase Genes: The enzyme responsible for cellulose biosynthesis (CesA) has similar genetic sequences in charophytes and land plants.
- Regulatory Genes: Some transcription factors crucial for land plant development, such as KNOX and BELL genes, have homologs in charophyte algae.
- Morphological and Structural Evidence
- Cell Division Similarities: Charophyte algae and land plants share a phragmoplast-based cell division mechanism, distinct from other algal groups.
- Sporopollenin Protection: Spores of early land plants and some charophytes are encased in sporopollenin, a tough biopolymer that protects against desiccation.
- Plasmodesmata: Both groups have plasmodesmata, cell-to-cell communication channels that enable coordinated growth.
- Branching Growth: Some charophyte algae, such as Coleochaete, show apical growth similar to land plants.
- Fossil Evidence
- Ordovician and Silurian Microfossils (470-440 Ma): Fossilized spores with sporopollenin coatings appear before macroscopic land plant fossils, indicating early adaptation to terrestrial environments.
- Rhynie Chert (Early Devonian, ~407 Ma): Preserves some of the earliest land plants (Rhynia, Aglaophyton), showing vascular tissue development.
- Cooksonia (Silurian-Devonian Transition, ~430-410 Ma): One of the earliest known vascular plants, showing transition from bryophyte-like ancestors to tracheophytes.
- Biochemical and Physiological Adaptations
- Desiccation Tolerance: Early land plants and some charophytes can survive drying out, an adaptation to terrestrial life.
- Hormonal Pathways: Land plants and charophytes use similar hormones, such as auxin and abscisic acid, for growth and stress response.
- Symbiosis with Fungi: Fossil evidence and molecular studies suggest that early land plants formed mutualistic associations with mycorrhizal fungi (Glomeromycota) to obtain nutrients.
- Transitional Forms
- Zygnematophyceae as a Key Group: Recent genomic studies suggest that the Zygnematophyceae, a subgroup of charophyte algae, are the closest relatives of land plants. These algae lack complex multicellularity but share stress tolerance genes with land plants.
- From Simple Algae to Complex Embryophytes: Gradual increase in structural complexity, from filamentous and parenchymatous algae to early non-vascular land plants, suggests a stepwise transition to terrestrial life.
The divergence of land plants from marine algae is well-supported by multiple independent lines of evidence. The transition was driven by adaptations to terrestrial challenges such as desiccation, nutrient acquisition, and reproduction. The evolutionary path likely involved early colonization by freshwater charophyte algae, which evolved desiccation tolerance, protective spores, and symbiotic relationships that facilitated the transition to permanent land-based life.