Genotype variation in rice (Oryza sativa L.) tolerance to Fe toxicity might be linked to root cell wall lignification

Iron (Fe) is an essential element to plants, but can be harmful if accumulated to toxic concentrations. Fe toxicity can be a major nutritional disorder in rice (Oryza sativa) when cultivated under waterlogged conditions, as a result of excessive Fe solubilization of in the soil. However, little is known about the basis of Fe toxicity and tolerance at both physiological and molecular level. To identify mechanisms and potential candidate genes for Fe tolerance in rice, we comparatively analyzed the effects of excess Fe on two cultivars with distinct tolerance to Fe toxicity, EPAGRI 108 (tolerant) and BR-IRGA 409 (susceptible). After excess Fe treatment, BR-IRGA 409 plants showed reduced biomass and photosynthetic parameters, compared to EPAGRI 108. EPAGRI 108 plants accumulated lower amounts of Fe in both shoots and roots compared to BR-IRGA 409. We conducted transcriptomic analyses of roots from susceptible and tolerant plants under control and excess Fe conditions. We found 423 up-regulated and 92 down-regulated genes in the susceptible cultivar, and 42 up-regulated and 305 down-regulated genes in the tolerant one. We observed striking differences in root gene expression profiles following exposure to excess Fe: the two cultivars showed no genes regulated in the same way (up or down in both), and 264 genes were oppositely regulated in both cultivars. Plants from the susceptible cultivar showed down-regulation of known Fe uptake-related genes, indicating that plants are actively decreasing Fe acquisition. On the other hand, plants from the tolerant cultivar showed up-regulation of genes involved in root cell wall biosynthesis and lignification. We confirmed that the tolerant cultivar has increased lignification in the outer layers of the cortex and in the vascular bundle compared to the susceptible cultivar, suggesting that the capacity to avoid excessive Fe uptake could rely in root cell wall remodeling. Moreover, we showed that increased lignin concentrations in roots might be linked to Fe tolerance in other rice cultivars, suggesting that a similar mechanism might operate in multiple genotypes. Our results indicate that changes in root cell wall and Fe permeability might be related to Fe toxicity tolerance in rice natural variation

Oryza sativa cv. Nipponbare and Oryza barthii as unexpected tolerance and susceptibility sources against Schizotetranychus oryzae (Acari: Tetranychidae) mite infestation

Cultivated rice (Oryza sativa L.) is frequently exposed to multiple stresses, including Schizotetranychus oryzae mite infestation. Rice domestication has narrowed the genetic diversity of the species, leading to a wide susceptibility. This work aimed to analyze the response of two African rice species (Oryza barthii and Oryza glaberrima), weedy rice (O. sativa f. spontanea), and O. sativa cv. Nipponbare to S. oryzae infestation. Surprisingly, leaf damage, histochemistry, and chlorophyll concentration/fluorescence indicated that the African species present a higher level of leaf damage, increased accumulation of H2O2, and lower photosynthetic capacity when compared to O. sativa plants under infested conditions. Infestation decreased tiller number, except in Nipponbare, and caused the death of O. barthii and O. glaberrima plants during the reproductive stage. While infestation did not affect the weight of 1,000 grains in both O. sativa, the number of panicles per plant was affected only in O. sativa f. spontanea, and the percentage of full seeds per panicle and seed length were increased only in Nipponbare. Using proteomic analysis, we identified 195 differentially abundant proteins when comparing susceptible (O. barthii) and tolerant (Nipponbare) plants under control and infested conditions. O. barthii presents a less abundant antioxidant arsenal and is unable to modulate proteins involved in general metabolism and energy production under infested condition. Nipponbare presents high abundance of detoxification-related proteins, general metabolic processes, and energy production, suggesting that the primary metabolism is maintained more active compared to O. barthii under infested condition. Also, under infested conditions, Nipponbare presents higher levels of proline and a greater abundance of defense-related proteins, such as osmotin, ricin B-like lectin, and protease inhibitors (PIs). These differentially abundant proteins can be used as biotechnological tools in breeding programs aiming at increased tolerance to mite infestation

Estudos sobre as proteínas ferritina e OsNRAMP7 em plantas de arroz (Oryza sativa L.)

O arroz é um dos cereais mais produzidos e consumidos no mundo, cultivado em aproximadamente 156 milhões de hectares, com uma produção mundial de mais de 600 milhões de toneladas por ano. O arroz é, hoje, alimento básico para mais de dois terços da população mundial. Contudo, minerais como ferro e zinco são perdidos durante o processo de beneficiamento dos grãos para comercialização. Uma vez que a deficiência de ferro afeta cerca de três bilhões de pessoas e é a deficiência mineral mais comum em humanos, diversos esforços têm sido feitos para aumentar a concentração deste mineral em grãos de arroz. Diversos projetos têm como objetivo compreender o mecanismo de translocação de nutrientes para grãos de arroz, visando o aumento de sua concentração com fins de biofortificação do alimento. Para melhor compreender a homeostase de ferro em plantas de arroz, conduzimos experimentos para analisar possíveis funções de duas proteínas. Proteínas da família NRAMP (Natural Resistance Associated Macrophage Protein) foram descritas como tendo envolvimento na homeostase de ferro em diferentes organismos. OsNRAMP7 apresenta propriedades características da família, como os motivos DPGN e MPH, possivelmente envolvidos no transporte de metais. Oócitos de Xenopus injetados com o mRNA de OsNRAMP7 apresentaram aumento significativo na concentração de ferro. A expressão heteróloga da proteína em oócitos indica o envolvimento da proteína no transporte transmembrana de ferro. Ferritina é outra proteína envolvida na homeostase de ferro nas células. Ferritinas são proteínas esféricas, capazes de armazenar ferro no seu interior, agindo também como um estoque de ferro nas células. O armazenamento de ferro dentro desta proteína pode prevenir reações que levam a produção de radicais livres e, consequentemente, estresse oxidativo. Duas cópias do gene da ferritina foram descritas em arroz. Respostas ao estresse oxidativo em uma linhagem mutante de arroz para o gene OsFER2 foram estudadas. Quando submetidas a excesso de ferro, plantas mutantes tiveram aumento na concentração de MDA (malondialdeído) nas partes aéreas e da atividade da enzima APX (ascorbato peroxidase) em raízes, revelando respostas ao dano oxidativo quando há baixa produção de ferritina. Plantas mutantes acumulam menos biomassa do que plantas WT (wild type) mesmo em condição controle de crescimento. Isso pode indicar um possível papel da ferritina na homeostase de ferro em plantas de arroz, ainda que as mesmas não estejam em estresse por excesso de ferro. Mecanismos compensatórios como o aumento da quantidade da proteína 5 frataxina e aumento do influxo de ferro para vacúolos também devem ser investigados. Mais experimentos são necessários para melhor compreensão do papel da ferritina na homeostase de ferro em arroz. Não obstante, com os experimentos aqui apresentados é possível determinar o envolvimento da proteína OsNRAMP7 na homeostase de ferro em arroz.Rice is one of the most produced and consumed cereals in the world, cultivated in approximately 156 million hectares, with a world production of over 600 million tons. It is a staple food for two thirds of the world population. However, minerals such as iron and zinc are lost during rice processing for commercialization. Since iron deficiency affects around three billion people, and is the most common mineral deficiency in humans, several efforts have been made in order to increase this nutrient’s levels in rice grains. Several projects have as goal to understand translocation mechanisms of nutrients to rice grains as to increase their levels for biofortification purposes. To better understand iron homeostasis in rice plants, we conducted experiments in order to analyze the putative role of two proteins. The NRAMP (Natural Resistance Associated Macrophage Protein) family was described as having an important role in iron homeostasis in different organisms. OsNRAMP7 presents characteristic features of the family, as motifs DPGN and MPH, said to be involved in metal transport. Xenopus oocytes injected with OsNRAMP7 mRNA exhibited a significant increase in iron content. Heterologous expression of the protein in oocytes indicated that the protein is involved in transmembrane iron transport. Ferritin is another protein involved in intracellular iron homeostasis. Ferritins are spherical proteins capable of storing iron in their core, also acting as an iron buffer in cells. Storage of free iron inside this protein may prevent reactions that lead to the formation of oxygen radicals and, therefore, to oxidative stress. Two ferritin genes have been described in the rice genome. We studied the oxidative stress response of a mutant line of rice with impaired expression of OsFer2. When subjected to iron excess, mutant plants increased MDA (malondialdehyde) concentration in shoots and APX (ascorbate peroxidase) enzyme activity in roots, revealing oxidative damage responses when ferritin production is impaired. Mutant plants have lower weight than WT (wild type) even in control growth condition. This may indicate a possible role of ferritin in iron homeostasis in rice plants, even when they are not under iron stress. Compensative mechanisms such as increase of frataxin levels and iron influx to the vacuole should be investigated. More experiments are required for a proper understanding of ferritin role in iron homeostasis. Still, with these experiments allowed to determine the involvement of the OsNRAMP7 protein in iron homeostasis in rice

Boletín meteorológico diario: Número 358 - 1981 Diciembre 24

Soil carbon accumulation is largely dependent on net primary productivity. To our knowledge, there have been no studies investigating the dynamics of carbon accumulation in weathered subtropical soils, especially in managed eucalyptus plantations. We quantified the seasonal input of leaf litter, the leaf decomposition rate and soil carbon stocks in an commercial plantation of Eucalyptus saligna Labill. in southern Brazil. Our goal was to evaluate, through multiple linear regression, the influence that certain chemical characteristics of litter, as well as chemical and physical characteristics of soil, have on carbon accumulation in soil organic matter fractions. Variables related to the chemical composition of litter were not associated with the soil carbon stock in the particulate and mineral fractions. However, certain soil characteristics were significantly associated with the carbon stock in both fractions. The concentrations of nutrients associated with plant growth and productivity, such as phosphorus, sulfur, copper and zinc, were associated with variations in the labile carbon pool (particulate fraction). Clay content was strongly associated with the carbon stock in the mineral fraction. The carbon accumulation and stabilization in weathered subtropical Ultisol seems to be mainly associated with the intrinsic characteristics of the soil, particularly clay content, rather than with the quantity, chemical composition or decomposition rate of the litter