Role In Symbiotic Associations Research Articles

The faster evolution of signal peptide genes of Frankia in surfactome may be attributed to their cardinal role in symbiotic association

The faster evolution of signal peptide genes of Frankia in surfactome may be attributed to their cardinal role in symbiotic association

Root economics spectrum and construction costs in Mediterranean woody plants: The role of symbiotic associations and the environment

Abstract Many studies have quantified the functional variation of fine root traits to understand the overarching trade‐off between maximizing resource acquisition or conservation (root economics spectrum [RES]). However, we know remarkably less on how plant strategies along the RES are actually constrained by the amount of photosynthates required to construct roots (i.e. construction costs, CC) or how below‐ground interactions with symbiotic organisms modify root trait patterns and their relationships with CC. Our main aim was to quantify CC of fine roots (<2 mm) and their underlying components (carbon, minerals and organic nitrogen concentrations) in 60 Mediterranean woody species with contrasting symbiotic association types (ectomycorrhizas, arbuscular and ericoid mycorrhizas and N‐fixing bacteria). We examined (a) whether the covariation among fine root traits along the RES was related to the intrinsic cost of producing roots and whether this relationship was dependent on the type of root symbiosis; (b) whether the relationship of each CC component with the RES was dependent on the type of root symbiosis and (c) whether soil water and nutrient availability determined differences in CC across sites. According to the RES hypothesis, fine root traits showed a main covariation trend (acquisition vs. conservation), defined by the first PCA axis, which also segregated species by their two main contrasting symbiotic types (arbuscular and ectomycorrhizal). We found a positive relationship between root CC and the RES (i.e. PCA axis 1) and, interestingly, slopes differed among symbiotic types, in response to the different role of each specific CC component. In addition, independently of symbiotic type, root CC decreased linearly with soil nutrient availability and quadratically with plant water availability. Synthesis. Our study demonstrates that woody plants display different functional strategies in their root CC, related with their position on the RES, and that CC differ among symbiotic groups. The influence of the root CC components across species varied among symbiotic associations, pointing to a trade‐off between structural and metabolic compounds. Root CC were also strongly modulated by soil resource availability (nutrients and water). This study highlights that root CC are fundamental to better understand below‐ground resource‐use strategies.

Glutaredoxins Play an Important Role in the Redox Homeostasis and Symbiotic Capacity of Azorhizobium caulinodans ORS571.

Glutaredoxin (GRX) plays an essential role in the control of the cellular redox state and related pathways in many organisms. There is limited information on GRXs from the model nitrogen (N2)-fixing bacterium Azorhizobium caulinodans. In the present work, we identified and performed functional analyses of monothiol and dithiol GRXs in A. caulinodans in the free-living state and during symbiosis with Sesbania rostrata. Our data show that monothiol GRXs may be very important for bacterial growth under normal conditions and in response to oxidative stress due to imbalance of the redox state in grx mutants of A. caulinodans. Functional redundancies were also observed within monothiol and dithiol GRXs in terms of different physiological functions. The changes in catalase activity and iron content in grx mutants were assumed to favor the maintenance of bacterial resistance against oxidants, nodulation, and N2 fixation efficiency in this bacterium. Furthermore, the monothiol GRX12 and dithiol GRX34 play a collective role in symbiotic associations between A. caulinodans and Sesbania rostrata. Our study provided systematic evidence that further investigations are required to understand the importance of glutaredoxins in A. caulinodans and other rhizobia.

Arbuscular mycorrhiza Symbiosis Induces a Major Transcriptional Reprogramming of the Potato SWEET Sugar Transporter Family.

Biotrophic microbes feeding on plants must obtain carbon from their hosts without killing the cells. The symbiotic Arbuscular mycorrhizal (AM) fungi colonizing plant roots do so by inducing major transcriptional changes in the host that ultimately also reprogram the whole carbon partitioning of the plant. AM fungi obtain carbohydrates from the root cortex apoplast, in particular from the periarbuscular space that surrounds arbuscules. However, the mechanisms by which cortical cells export sugars into the apoplast for fungal nutrition are unknown. Recently a novel type of sugar transporter, the SWEET, able to perform not only uptake but also efflux from cells was identified. Plant SWEETs have been shown to be involved in the feeding of pathogenic microbes and are, therefore, good candidates to play a similar role in symbiotic associations. Here we have carried out the first phylogenetic and expression analyses of the potato SWEET family and investigated its role during mycorrhiza symbiosis. The potato genome contains 35 SWEETs that cluster into the same four clades defined in Arabidopsis. Colonization of potato roots by the AM fungus Rhizophagus irregularis imposes major transcriptional rewiring of the SWEET family involving, only in roots, changes in 22 of the 35 members. None of the SWEETs showed mycorrhiza-exclusive induction and most of the 12 induced genes belong to the putative hexose transporters of clade I and II, while only two are putative sucrose transporters from clade III. In contrast, most of the repressed transcripts (10) corresponded to clade III SWEETs. Promoter-reporter assays for three of the induced genes, each from one cluster, showed re-localization of expression to arbuscule-containing cells, supporting a role for SWEETs in the supply of sugars at biotrophic interfaces. The complex transcriptional regulation of SWEETs in roots in response to AM fungal colonization supports a model in which symplastic sucrose in cortical cells could be cleaved in the cytoplasm by sucrose synthases or cytoplasmic invertases and effluxed as glucose, but also directly exported as sucrose and then converted into glucose and fructose by cell wall-bound invertases. Precise biochemical, physiological and molecular analyses are now required to profile the role of each potato SWEET in the arbuscular mycorrhizal symbiosis.

Nitric oxide and heat shock protein 90 co-regulate temperature-induced bleaching in the soft coral Eunicea fusca

Coral bleaching represents a complex physiological process that is affected not only by environmental conditions but by the dynamic internal cellular biology of symbiotic dinoflagellates (Symbiodinium spp.) and their cnidarian hosts. Recently, nitric oxide (NO) has emerged as a key molecule involved with the expulsion of Symbiodinium from host cnidarian cells. However, the site of production remains under debate, and the corresponding signaling pathways within and between host and endosymbiont remain elusive. In this study, using freshly isolated Symbiodinium from the soft coral Eunicea fusca, I demonstrate that thermally induced stress causes an upregulation in Symbiodinium heat shock protein 90 (Hsp90). In turn, Hsp90 shows a concomitant ability to enhance the activity of a constitutively expressed isoform of NO synthase. The resulting production of NO constitutes a signaling molecule capable of inducing Symbiodinium expulsion. Using nitric oxide synthase (NOS) and Hsp90 polyclonal antibodies, thermal stress-induced Hsp90 was shown to co-immunoprecipitate with a constitutive isoform of NOS. The specific blocking of Hsp90 activity, with the Hsp90 inhibitor geldanamycin, was capable of inhibiting NO production implicating the involvement of a coordinated regulatory system. These results have strong evolutionary implications for Hsp90–NOS chaperone complexes among biological kingdoms and provide evidence for a new functional role in symbiotic associations.

NUTRITIONAL STRATEGIES OF SUBMERGED BENTHIC PLANTS: THE ACQUISITION OF C, N AND P BY RHIZOPHYTES AND HAPTOPHYTES

Submerged benthic plants (algae and ‘higher plants’) can be classified into two groups on the basis of their attachment to the substrate. ‘Haptophytes’ are attached to the surface of rocks; ‘Rhizophytes’ have rhizoids, roots or rhizomes within the substratum (sand or mud). Haptophytes must obtain all of their nutrients from the bulk water phase, while rhizophytes can obtain some of their nutrients from the sediment. Evidence as to the sites of nutrient uptake on the surface of rhizophytes supports the view that a substantial fraction of phosphorus and nitrogen and, in some cases, inorganic carbon, is obtained from the sediment. This might be expected to make the portion of the rhizophyte which occurs in the bulk water phase more specialized for interception of photosynthetic light and C than the corresponding portion of the haptophyte which also intercepts and absorbs all other mineral nutrients. The morphology of the haptophyte and its frequent occurrence in more rapidly flowing water means that the superficial unstirred layer is less of an impedance to nutrient transport from the bulk medium to the plant surface. This in turn improves the supply of inorganic C, which is reflected in more negative delta 13C values and higher biochemical capacities for photosynthesis per unit plant surface in haptophytes than in rhizophytes. Haptophytes frequently have colourless hairs on their surface, especially in media of low nutrient content or with poor water movement: in many cases, these hairs seem to be involved in nutrient uptake. Despite their different mechanisms for uptake of nutrients, rhizophytes and haptophytes can produce similar biomasses and chlorophyll m−2, although rhizophytes may have rather lower productivities. The role of symbiotic associations (mycorrhizas in vascular plants; microalgae in invertebrates) in uptake of nutrients and photosynthesis is discussed in relation to haptophytic and rhizophytic strategies, as is the evolution of land plants.