RESUMO
Arbuscular mycorrhizal (AM) fungi and rhizobia form two of the most important plant-microbe associations for the assimilation of phosphorus (P) and nitrogen (N). Symbiont-derived signals are able to coordinate the infection process by triggering multiple responses in the plant root, such as calcium influxes and oscillations, increased reactive oxygen species (ROS), cytoskeletal rearrangements and altered gene expression. An examination was made of the role of tetraspanins, which are transmembrane proteins that self-organize into tetraspanin web regions, where they recruit specific proteins into platforms required for signal transduction, membrane fusion, cell trafficking, and ROS generation. In plant cells, tetraspanins are scaffolding proteins associated with root radial patterning, biotic and abiotic stress responses, cell fate determination, plasmodesmata and hormonal regulation. Some plant tetraspanins, such as Arabidopsis thaliana TETRASPANIN 8 and TETRASPANIN 9 (AtTET8 and AtTET9) are associated with exosomes during inter-kingdom communication. In this study, a homolog of AtTET8, PvTET8-1, in common bean (Phaseolus vulgaris L. var. Negro Jamapa) was examined in roots during interactions with Rhizobium tropici and Rhizophagus irregularis. The promoter of PvTET8-1 contained several cis-acting regulatory DNA elements potentially related to mutualistic interactions, and PvTET8-1 was transcriptionally activated during AM fungal and rhizobial associations. Silencing it decreased the size and number of nodules, nitrogen fixation, and mycorrhizal arbuscule formation, whereas overexpressing it increased the size and number of nodules, and mycorrhizal arbuscule formation but decreased nitrogen fixation. PvTET8-1 appears to be an important element in both of these mutualistic interactions, perhaps through its interaction with NADPH oxidase and the generation of ROS during the infection processes.
RESUMO
A genome-wide analysis identified the set of small RNAs (sRNAs) from the agronomical important legume Phaseolus vulgaris (common bean), including novel P. vulgaris-specific microRNAs (miRNAs) potentially important for the regulation of the rhizobia-symbiotic process. Generally, novel miRNAs are difficult to identify and study because they are very lowly expressed in a tissue- or cell-specific manner. In this work, we aimed to analyze sRNAs from common bean root hairs (RH), a single-cell model, induced with pure Rhizobium etli nodulation factors (NF), a unique type of signal molecule. The sequence analysis of samples from NF-induced and control libraries led to the identity of 132 mature miRNAs, including 63 novel miRNAs and 1984 phasiRNAs. From these, six miRNAs were significantly differentially expressed during NF induction, including one novel miRNA: miR-RH82. A parallel degradome analysis of the same samples revealed 29 targets potentially cleaved by novel miRNAs specifically in NF-induced RH samples; however, these novel miRNAs were not differentially accumulated in this tissue. This study reveals Phaseolus vulgaris-specific novel miRNA candidates and their corresponding targets that meet all criteria to be involved in the regulation of the early nodulation events, thus setting the basis for exploring miRNA-mediated improvement of the common bean-rhizobia symbiosis.
Assuntos
Regulação da Expressão Gênica de Plantas , MicroRNAs/genética , Phaseolus/genética , Nodulação/genética , Raízes de Plantas/genética , Interferência de RNA , RNA Mensageiro/genética , Biologia Computacional/métodos , Sequenciamento de Nucleotídeos em Larga Escala , Análise de Sequência de DNARESUMO
The symbiotic interaction of legumes and rhizobia results in the formation of nitrogen-fixing nodules. Nodulation depends on the finely coordinated expression of a battery of genes involved in the infection and the organogenesis processes. After Nod factor perception, symbiosis receptor kinase (SymRK) receptor triggers a signal transduction cascade essential for nodulation leading to cortical cell divisions, infection thread (IT) formation and final release of rhizobia to the intracellular space, forming the symbiosome. Herein, the participation of SymRK receptor during the nodule organogenesis in Phaseolus vulgaris is addressed. Our findings indicate that besides its expression in the nodule epidermis, in IT, and in uninfected cells of the infection zone, PvSymRK immunolocalizes in the root and nodule vascular system. On the other hand, knockdown expression of PvSymRK led to the formation of scarce and defective nodules, which presented alterations in both IT/symbiosome formation and vascular system.