Abstract
Arbuscular mycorrhizal fungi and rhizobia association with plants are two of the most successful plant-microbe associations that allow the assimilation of P and N by plants, respectively. These mutualistic interactions require a molecular dialogue, i.e., legume roots exude flavonoids or strigolactones which induce the Nod factors or Myc factors synthesis and secretion from the rhizobia or fungi, respectively. These Nod or Myc factors trigger several responses in the plant root, including calcium oscillations, and reactive oxygen species (ROS). Furthermore, superoxide and H2O2 have emerged as key components that regulate the transitions from proliferation to differentiation in the plant meristems. Similar to the root meristem, the nodule meristem accumulates superoxide and H2O2. Tetraspanins are transmembrane proteins that organize into tetraspanin web regions, where they recruit specific proteins into platforms required for signal transduction, membrane fusion, cell trafficking and ROS generation. Plant tetraspanins are scaffolding proteins associated with root radial patterning, biotic and abiotic stress responses, cell fate determination, and hormonal regulation and recently have been reported as a specific marker of exosomes in animal and plant cells and key players at the site of plant fungal infection. In this study, we conducted transcriptional profiling of the tetraspanin family in common bean (Phaseolus vulgaris L. var. Negro Jamapa) to determine the specific expression patterns and subcellular localization of tetraspanins during nodulation or under mycorrhizal association. Our results demonstrate that the tetraspanins are transcriptionally modulated during the mycorrhizal association, but are also expressed in the infection thread and nodule meristem development. Subcellular localization indicates that tetraspanins have a key role in vesicular trafficking, cell division, and root hair polar growth.
Highlights
The symbiotic interaction between rhizobia and legumes requires a molecular dialogue that involves the exchange of specific signaling molecules
Since PvTET8 was highly induced during nodulation, but not during mycorrhizal association, we suggest that this tetraspanin plays a particular role during nodulation, including the infection thread formation
AtTET10 and OsTET14 from O. sativa can be considered the founders of the tetraspanin family in their respective species [35, 50]
Summary
The symbiotic interaction between rhizobia and legumes requires a molecular dialogue that involves the exchange of specific signaling molecules. Thereafter, NFs or Myc factors are recognized by the plant root and induce several responses, including ionic changes, membrane depolarization, cytoskeleton rearrangements, reactive oxygen species (ROS) generation, and gene expression [4,5,6,7]. While the bacteria travel inside the IT through the root hair, the cortical cells divide in a NF-dependent manner to form the nodule primordia that the rhizobia colonize in structures named symbiosome. The arbuscular mycorrhizal association induces the hypopodium and the further invasion of the cortical cells, which end up with the arbuscule formation Both processes, the bacterial colonization trough the infection thread and arbuscule formation, require an active vesicular trafficking, endocytosis and exocytosis in order to increase the membranal surface required for symbiosome and arbuscule formation [16, 17]
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