In Vivo Metabolic Regulation of Alternative Oxidase under Nutrient Deficiency—Interaction with Arbuscular Mycorrhizal Fungi and Rhizobium Bacteria

The interaction of the alternative oxidase (AOX) pathway with nutrient metabolism is important for understanding how respiration modulates ATP synthesis and carbon economy in plants under nutrient deficiency. Although AOX activity reduces the energy yield of respiration, this enzymatic activity is upregulated under stress conditions to maintain the functioning of primary metabolism. The in vivo metabolic regulation of AOX activity by phosphorus (P) and nitrogen (N) and during plant symbioses with Arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria is still not fully understood. We highlight several findings and open questions concerning the in vivo regulation of AOX activity and its impact on plant metabolism during P deficiency and symbiosis with AMF. We also highlight the need for the identification of which metabolic regulatory factors of AOX activity are related to N availability and nitrogen-fixing legume-rhizobia symbiosis in order to improve our understanding of N assimilation and biological nitrogen fixation.FONDECYT from National Agency for Research and Development (ANID) 1191118Chilean Scholarship Program/Becas de doctorado nacional/2017 21180329European Union (EU) 75330

Nitrogen sources differentially affect respiration, growth, and carbon allocation in Andean and Lowland ecotypes of Chenopodium quinoa Willd

Chenopodium quinoa Willd. is a native species that originated in the High Andes plateau (Altiplano) and its cultivation spread out to the south of Chile. Because of the different edaphoclimatic characteristics of both regions, soils from Altiplano accumulated higher levels of nitrate (NO3−) than in the south of Chile, where soils favor ammonium (NH4+) accumulation. To elucidate whether C. quinoa ecotypes differ in several physiological and biochemical parameters related to their capacity to assimilate NO3− and NH4+, juvenile plants of Socaire (from Altiplano) and Faro (from Lowland/South of Chile) were grown under different sources of N (NO3− or NH4+). Measurements of photosynthesis and foliar oxygen-isotope fractionation were carried out, together with biochemical analyses, as proxies for the analysis of plant performance or sensitivity to NH4+. Overall, while NH4+ reduced the growth of Socaire, it induced higher biomass productivity and increased protein synthesis, oxygen consumption, and cytochrome oxidase activity in Faro. We discussed that ATP yield from respiration in Faro could promote protein production from assimilated NH4+ to benefit its growth. The characterization of this differential sensitivity of both quinoa ecotypes for NH4+ contributes to a better understanding of nutritional aspects driving plant primary productivity

Structural plasticity in root-fungal symbioses: diverse interactions lead to improved plant fitness

Root-fungal symbioses such as mycorrhizas and endophytes are key components of terrestrial ecosystems. Diverse in trophy habits (obligate, facultative or hemibiotrophs) and symbiotic relations (from mutualism to parasitism), these associations also show great variability in their root colonization and nutritional strategies. Specialized interface structures such as arbuscules and Hartig nets are formed by certain associations while others are restricted to non-specialized intercellular or intracellular hyphae in roots. In either case, there are documented examples of active nutrient exchange, reinforcing the fact that specialized structures used to define specific mycorrhizal associations are not essential for reciprocal exchange of nutrients and plant growth promotion. In feremycorrhiza (with Austroboletus occidentalis and eucalypts), the fungal partner markedly enhances plant growth and nutrient acquisition without colonizing roots, emphasizing that a conventional focus on structural form of associations may have resulted in important functional components of rhizospheres being overlooked. In support of this viewpoint, mycobiome studies using the state-of-the-art DNA sequencing technologies have unearthed much more complexity in root-fungal relationships than those discovered using the traditional morphology based approaches. In this review, we explore the existing literature and most recent findings surrounding structure, functioning, and ecology of root-fungal symbiosis, which highlight the fact that plant fitness can be altered by taxonomically/ecologically diverse fungal symbionts regardless of root colonization and interface specialization. Furthermore, transition from saprotrophy to biotrophy seems to be a common event that occurs in diverse fungal lineages (consisting of root endophytes, soil saprotrophs, wood decayers etc.), and which may be accompanied by development of specialized interface structures and/or mycorrhiza-like effects on plant growth and nutrition

The Symbiosome: Legume and Rhizobia Co-evolution toward a Nitrogen-Fixing Organelle?

In legume nodules, symbiosomes containing endosymbiotic rhizobial bacteria act as temporary plant organelles that are responsible for nitrogen fixation, these bacteria develop mutual metabolic dependence with the host legume. In most legumes, the rhizobia infect post-mitotic cells that have lost their ability to divide, although in some nodules cells do maintain their mitotic capacity after infection. Here, we review what is currently known about legume symbiosomes from an evolutionary and developmental perspective, and in the context of the different interactions between diazotroph bacteria and eukaryotes. As a result, it can be concluded that the symbiosome possesses organelle-like characteristics due to its metabolic behavior, the composite origin and differentiation of its membrane, the retargeting of host cell proteins, the control of microsymbiont proliferation and differentiation by the host legume, and the cytoskeletal dynamics and symbiosome segregation during the division of rhizobia-infected cells. Different degrees of symbiosome evolution can be defined, specifically in relation to rhizobial infection and to the different types of nodule. Thus, our current understanding of the symbiosome suggests that it might be considered a nitrogen-fixing link in organelle evolution and that the distinct types of legume symbiosomes could represent different evolutionary stages toward the generation of a nitrogen-fixing organelle

Legumes in the reclamation of marginal soils, from cultivar and inoculant selection to transgenic approaches

18 páginas, ilustraciones y tablas estadísticas.Mineral nitrogen deficiency is a frequent characteristic of arid and semi-arid soils....Peer reviewe

Molecular characterization and expression patterns of peroxiredoxin V (PrxV) from the scallop Argopecten purpuratus after Vibrio splendidus challenge

The scallop Argopecten purpuratus is a species of importance for aquaculture in Chile and Peru, but in recent years, they have decreased their growth rates and experienced massive mortalities potentially associated with pathogenic infections. Characterization of proteins involved in the immunity status of A. purpuratus is of interest to develop molecular markers to support its culture. Here we report the characterization of a new Peroxiredoxin (Prx) homologue, the first one identified in A. purpuratus. Prxs are a ubiquitous family of cysteine-dependent peroxidase enzymes that play a dominant role in the regulation of peroxide levels in cells, as rapidly detoxify peroxynitrite, hydrogen peroxide and organic hydroperoxides. The molecular and phylogenetic analyses of this gene showed that it is a new member of the PrxV family, thus, it was designated as ApPrxV. This gene showed to be constitutively expressed in each examined tissue, but at a higher level in the striated adductor muscle. ApPrxV expression was highly upregulated in haemocytes in response to an immune challenge with pathogen bacteria Vibrio splendidus. Overall results indicate that ApPrxV is a constitutive and inducible protein that can play an important role in the immune response of A. purpuratus against bacterial infection. Therefore, the results of this study can (i) provide the bases for future functional studies to assess the health status of A. purpuratus; and (ii) can guide the development of molecular markers for future selective breeding of this bivalve

Rapid screening of Medicago truncatula germplasm for mercury tolerance at the seedling stage

13 paginas, 4 figuras y 4 tablas estadísticasThe development of novel phytoremediation strategies to mitigate mercury contamination, an increasingly important worldwide threat, could be enhanced by identifying Hg-tolerant legume cultivars. A fast method was thus developed to screen a germplasm collection of the model legume Medicago truncatula for Hg tolerance, testing 258 accessions at the seedling stage in a miniaturized hydroponic system and using root growth as an indicator of tolerance. To validate the results of the screening, the Hg-tolerant cultivars identified were analyzed in a referenced hydroponic growth assay. The different growth parameters measured in this assay were then subjected to a factorial analysis (principal component analysis method) in order to establish indices of tolerance, which further supported the rapid method of screening. Accordingly, four Hg-tolerant M. truncatula cultivars were selected that might serve as source material for genetic improvement, as model cultivars to study Hg tolerance in legumes and/or to develop soil phytoremediation approaches.Peer reviewe

Salt tolerance in the Rhizobium-legume symbiosis: An overview

18 pages, figures, and tables statistics.High salinity in soils induces a strong decrease in crop yield and productivity in arable land. Plants can develop tolerance mechanisms to overcome salt and environmental stresses, including changes in gene expression patterns and in metabolic homeostasis.Peer reviewe

Alfalfa nodules elicited by a flavodoxin-overexpressing Ensifer meliloti strain display nitrogen-fixing activity with enhanced tolerance to salinity stress

14 páginas y 7 figurasNitrogen fixation by legumes is very sensitive to salinity stress, which can severely reduce the productivity of legume crops and their soil-enriching capacity. Salinity is known to cause oxidative stress in the nodule by generating reactive oxygen species (ROS). Flavodoxins are involved in the response to oxidative stress in bacteria and cyanobacteria. Prevention of ROS production by flavodoxin overexpression in bacteroids might lead to a protective effect on nodule functioning under salinity stress. Tolerance to salinity stress was evaluated in alfalfa nodules elicited by an Ensifer meliloti strain that overexpressed a cyanobacterial flavodoxin compared with nodules produced by the wildtype bacteria. Nitrogen fixation, antioxidant and carbon metabolism enzyme activities were determined. The decline in nitrogenase activity associated to salinity stress was significantly less in flavodoxin-expressing than in wild-type nodules.We detected small but significant changes in nodule antioxidant metabolism involving the ascorbate–glutathione cycle enzymes and metabolites, as well as differences in activity of the carbon metabolism enzyme sucrose synthase, and an atypical starch accumulation pattern in flavodoxincontaining nodules. Salt-induced structural and ultrastructural alterations were examined in detail in alfalfa wild-type nodules by light and electron microscopy and compared to flavodoxin-containing nodules. Flavodoxin reduced saltinduced structural damage, which primarily affected young infected tissues and not fully differentiated bacteroids. The results indicate that overexpression of flavodoxin in bacteroids has a protective effect on the function and structure of alfalfa nodules subjected to salinity stress conditions. Putative protection mechanisms are discussedPeer reviewe