29.3 Bryophytes and Microorganisms
Bryophytes (non-vascular plants), including mosses, liverworts, and hornworts, and
traqueophytes (vascular plants; lycophytes, ferns, gymnosperms and angiosperms),
evolved from early land plants. Extant bryophytes represent therefore excellent
model organisms to reveal ancient mechanisms related to plant–microorganism
interactions. In addition, comparative analysis with tracheophyte lineages contributes to shed light on the origin and evolution of key land plant innovations during
biotic interactions. As fascinating windows to the past, several fossil records from
Ordovician sediments have shown the presence of fungal structures associated with
early bryophytes, demonstrating the existence of ancient interactions that could
persist nowadays. Arbuscular mycorrhizal (AM) fungi belonging to the groups
Glomeromycotina and Mucoromycotina have been reported in bryophytes fossils
(Strullu-Derrien et al. 2014). Both types of fungi are proposed to be implicated in
land colonization by plants. Extant liverworts and hornworts also establish symbiotic
associations with both types of fungi, sometimes simultaneously. The interaction
with these AM fungi, as well as association with endophytic members of the
ascomycota and basidiomycota groups, improves bryophyte growth and fitness
through enhanced nutrient uptake. The AM fungi colonize the tissues of liverworts
forming structures that are analogous to those observed in AM colonized roots of
vascular plants, including intracellular hyphae, arbuscule-like structures, and vesicles. At present, plant symbiosis with both Glomeromycotina and Mucoromycotina
are common in agricultural and natural ecosystems. The association of these fungal
groups with different plant lineages has persisted during 450 million years of
coevolution demonstrating a clear functional advantage. Thus, why are there no
evidences that suggest the existence of a functional symbiosis with mosses and AM
fungi? This is an intriguing issue and a plausible explanation is the loss of some
symbiotic signaling genes in mosses.
Diverse microbial pathogens colonize bryophytes, including fungi, bacteria,
oomycetes, and viruses. Several fungi and bacteria have been isolated from wild
population of mosses and liverworts. In addition, wide host range pathogens that
infect crops also colonize and cause disease in some of these bryophytes (Fig. 29.1),
allowing comparative studies of defense activation and strategies developed by the
pathogen to interfere with plant immunity.
29.4 Coevolution of Plants and Microorganisms
In the last 20 years, progress in understanding molecular aspects of coevolution of
traqueophytes with their associated microorganisms has revealed complex responses
on both sites. Plants have developed mechanisms to detect the presence of a
microorganism, distinguish if the microbe is beneficial or pathogenic, and mount a
response accordingly. Receptors at the plasma membrane act as sentinels and
29 Coevolution of Bryophytes and their Associated Microorganisms
629
Bryophytes (non-vascular plants), including mosses, liverworts, and hornworts, and
traqueophytes (vascular plants; lycophytes, ferns, gymnosperms and angiosperms),
evolved from early land plants. Extant bryophytes represent therefore excellent
model organisms to reveal ancient mechanisms related to plant–microorganism
interactions. In addition, comparative analysis with tracheophyte lineages contributes to shed light on the origin and evolution of key land plant innovations during
biotic interactions. As fascinating windows to the past, several fossil records from
Ordovician sediments have shown the presence of fungal structures associated with
early bryophytes, demonstrating the existence of ancient interactions that could
persist nowadays. Arbuscular mycorrhizal (AM) fungi belonging to the groups
Glomeromycotina and Mucoromycotina have been reported in bryophytes fossils
(Strullu-Derrien et al. 2014). Both types of fungi are proposed to be implicated in
land colonization by plants. Extant liverworts and hornworts also establish symbiotic
associations with both types of fungi, sometimes simultaneously. The interaction
with these AM fungi, as well as association with endophytic members of the
ascomycota and basidiomycota groups, improves bryophyte growth and fitness
through enhanced nutrient uptake. The AM fungi colonize the tissues of liverworts
forming structures that are analogous to those observed in AM colonized roots of
vascular plants, including intracellular hyphae, arbuscule-like structures, and vesicles. At present, plant symbiosis with both Glomeromycotina and Mucoromycotina
are common in agricultural and natural ecosystems. The association of these fungal
groups with different plant lineages has persisted during 450 million years of
coevolution demonstrating a clear functional advantage. Thus, why are there no
evidences that suggest the existence of a functional symbiosis with mosses and AM
fungi? This is an intriguing issue and a plausible explanation is the loss of some
symbiotic signaling genes in mosses.
Diverse microbial pathogens colonize bryophytes, including fungi, bacteria,
oomycetes, and viruses. Several fungi and bacteria have been isolated from wild
population of mosses and liverworts. In addition, wide host range pathogens that
infect crops also colonize and cause disease in some of these bryophytes (Fig. 29.1),
allowing comparative studies of defense activation and strategies developed by the
pathogen to interfere with plant immunity.
29.4 Coevolution of Plants and Microorganisms
In the last 20 years, progress in understanding molecular aspects of coevolution of
traqueophytes with their associated microorganisms has revealed complex responses
on both sites. Plants have developed mechanisms to detect the presence of a
microorganism, distinguish if the microbe is beneficial or pathogenic, and mount a
response accordingly. Receptors at the plasma membrane act as sentinels and
29 Coevolution of Bryophytes and their Associated Microorganisms
629