the host plants and the microorganisms develop to be successful? All these types of
questions are starting to be answered by using fossil records and extant land plants,
including bryophytes.
29.2 In the Beginning
Descendants of freshwater algae colonized terrestrial habitats long time ago in the
Late Ordovician period, approximately 450 million years ago (Mya). At that time,
the world was a barren place covered by rocks. The conquest of land by plants was
one of the most important steps in the evolution of life on earth and the foundation of
ecosystems. It changed the planet completely by reshaping the global environment,
including land, oceans, and the atmosphere. However, the transition from an aquatic
to a terrestrial habitat was not easy since it presented numerous challenges related to
nutrient and water acquisition. In addition, environmental conditions changed dramatically, leading to desiccation, extreme temperatures, and ultraviolet radiation
exposition. To survive these environmental stresses, the first land plants (embryophytes) developed different adaptation mechanisms. Cuticles and cell walls
supported dehydration stress, and metabolites such as phenylpropanoids acted as
shields against UV irradiance. Furthermore, things are always easier when you have
a partner, and highly preserved fossils from this period have shown that embryophytes did not colonize the land alone. The presence of fungal structures in these
fossils suggests that beneficial associations facilitated land colonization (Remy et al.
1994). The improvement of nutrient capture by plants was probably the main reason.
In exchange for inorganic nutrients obtained from soil and water, early land plants
provided photosynthesis-derived carbohydrates to the fungi. These interactions
evolved into symbioses, and nowadays most land plants establish mutualistic symbiosis with fungi.
However, pathogenic microorganisms present in soil and air also composed the
new terrestrial habitat. Fossil records suggest the existence of pathogenic fungi
interacting with plants 400 Mya (Krings et al. 2007). These microorganisms might
have imposed a selective pressure on early land plants leading to the development of
defensive strategies to counteract invasion. During time, both plants and pathogens
have evolved mechanism to avoid each other’s defense strategies. This evolutionary
arms race between plants and pathogens has resulted in the development of specialized and effective plant defense mechanisms and in adaptation strategies of the
pathogen to changes occurring in host plants.
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G. Reboledo and I. Ponce de León
questions are starting to be answered by using fossil records and extant land plants,
including bryophytes.
29.2 In the Beginning
Descendants of freshwater algae colonized terrestrial habitats long time ago in the
Late Ordovician period, approximately 450 million years ago (Mya). At that time,
the world was a barren place covered by rocks. The conquest of land by plants was
one of the most important steps in the evolution of life on earth and the foundation of
ecosystems. It changed the planet completely by reshaping the global environment,
including land, oceans, and the atmosphere. However, the transition from an aquatic
to a terrestrial habitat was not easy since it presented numerous challenges related to
nutrient and water acquisition. In addition, environmental conditions changed dramatically, leading to desiccation, extreme temperatures, and ultraviolet radiation
exposition. To survive these environmental stresses, the first land plants (embryophytes) developed different adaptation mechanisms. Cuticles and cell walls
supported dehydration stress, and metabolites such as phenylpropanoids acted as
shields against UV irradiance. Furthermore, things are always easier when you have
a partner, and highly preserved fossils from this period have shown that embryophytes did not colonize the land alone. The presence of fungal structures in these
fossils suggests that beneficial associations facilitated land colonization (Remy et al.
1994). The improvement of nutrient capture by plants was probably the main reason.
In exchange for inorganic nutrients obtained from soil and water, early land plants
provided photosynthesis-derived carbohydrates to the fungi. These interactions
evolved into symbioses, and nowadays most land plants establish mutualistic symbiosis with fungi.
However, pathogenic microorganisms present in soil and air also composed the
new terrestrial habitat. Fossil records suggest the existence of pathogenic fungi
interacting with plants 400 Mya (Krings et al. 2007). These microorganisms might
have imposed a selective pressure on early land plants leading to the development of
defensive strategies to counteract invasion. During time, both plants and pathogens
have evolved mechanism to avoid each other’s defense strategies. This evolutionary
arms race between plants and pathogens has resulted in the development of specialized and effective plant defense mechanisms and in adaptation strategies of the
pathogen to changes occurring in host plants.
628
G. Reboledo and I. Ponce de León