Phosphate solubilization by Antarctic yeasts isolated from lichens.

Antarctica has a great diversity of microorganisms with biotechnological potential but is not very well Known about yeasts with phosphate solubilization activity. Thus, the aim of this study was to evaluate the ability of yeasts from Antarctica lichens to solubilize phosphate in vitro. In the screening, 147 yeasts were tested and 43 (29%) showed P solubilization in solid NBRIP medium at 15.0 °C, with a higher prevalence of positive genera Vishniacozyma, followed by Cystobasidium. Most of the positive yeasts were isolated from Usnea auratiacoatra, followed by Polycauliona regalis and Lecania brialmontii. Two strains with better activity after screening were selected for the solubilization in the liquid medium, Vishniacozyma victoriae 2.L15 and A.L6 (unidentified). Vishniacozyma victoriae 2.L15 exhibiting activities at 25.0 °C (29.91 mg/L of phosphate and pH 6.85) and at 30.0 °C (619.04 mg/L of phosphate and pH 3.73) and A.L6 strain at 25.0 °C (25.05 mg/L of phosphate and pH 6.69) and at 30.0 °C (31.25 mg/L of phosphate and pH 6.47). Of eight organic acids tested by HPLC, tartaric and acetic acids were detected during phosphate solubilization, with greater release in the period of 144 (2.13 mg/L) and 72 (13.72 mg/L) hours, respectively. Future studies to elucidate the presence of functional genes for P metabolism in lichens, as well as studies in the field of proteomics for the discovery of yeast proteins related to P solubilization are needed. Thus, the high prevalence of lichen-associated yeast communities probably contributed to the high frequency of phosphate-solubilizing isolates in this study.

Antarctic lichens as a source of phosphate-solubilizing bacteria.

In association with lichens, bacteria can play key roles in solubilizing sources of inorganic phosphates that are available in the environment. In this study, the potential of bacteria isolated from 15 Antarctic lichen samples for phosphate solubilization was investigated. From 124 bacteria tested, 66 (53%) were positive for phosphate solubilization in solid NBRIP medium, with a higher prevalence of Pseudomonas, followed by Caballeronia and Chryseobacterium. Most of the phosphate-solubilizing bacteria were isolated from Usnea auratiacoatra, followed by Caloplaca regalis and Xanthoria candelaria. Two isolates showed outstanding performance, Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, since they presented solubilization in the temperature range from 15.0 to 30.0 °C, and maximum quantification of soluble phosphate at 25.0 °C was 511.21 and 532.07 mg/L for Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, respectively. At 30.0 °C soluble phosphate yield was 639.43 and 518.95 mg/L with pH of 3.74 and 3.87 for Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, respectively. Fumaric and tartaric acids were released during the solubilization process. Finally, bacteria isolated from Antarctic lichens were shown to have the potential for phosphate solubilization, opening perspectives for future application in the agricultural sector and contributing to reduce the use of chemical fertilizers.

An efficient antioxidant system is associated with lower photosynthesis photoinhibition and greater toleranc e to drought in sugarcane cultivars / Um eficiente sistema antioxidante está associado a menor fotoinibição da fotossíntese e maior tolerância à seca em cultivares de cana-de-açúcar

The occurrence of seasonal droughts is one of the main factors that limit the sugarcane ratoon cycles, compromising sugarcane field longevity. The aim of this study was to evaluate the biochemical responses of sugarcane cultivars to drought stress in ratoon crop. Six cultivars were used: RB72910, RB99382, RB72454, RB92579, RB855536 and RB931011, and three water regimes based on soil available water content(SAWC) and defined as: control, 80 to 100% (SAWC); moderate water stress, 40 to 60% (SAWC), and severewater stress, 0 to 20% (SAWC). Cultivar RB72454 was most sensitive to water deficit. When under stress, this cultivar showed an increased production of hydrogen peroxide, but without concomitant increase in the activity of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase. Oxidative stress led to lipid peroxidation and chlorophyll degradation, resulting in higher photochemical photoinhibition. On the other hand, cultivar RB92579 was the most tolerant to drought, with increased activity of antioxidant enzymes, which led to low lipid peroxidation, maintenance of photosynthetic pigments and photochemical activity. The antioxidant defense system triggered by ascorbate peroxidase, catalase and superoxide dismutase enzymes appears to be a key protection factor to photochemical complexes of chloroplast of sugarcane plants under water stress. The increase in the antioxidant system as well as the maintenance of photosynthetic pigments and cell membranes served as important criteria to indicate cultivars more tolerant to drought stress.

A ocorrência de secas sazonais é um dos principais fatores que limitam a longevidade do canavial. Esse trabalho teve como objetivo avaliar as respostas bioquímicas de cultivares de cana-de-açúcar em seu segundo ciclo de cultivo a condições de estresse hídrico. Para tanto, foram utilizadas seis cultivares: RB72910, RB99382, RB72454, RB92579, RB855536 e RB931011, e três regimes hídricos, baseado na capacidade de água disponível (CAD) e definidos como: controle, 80 a 100% (CAD); estresse hídrico moderado, 40 a 60% (CAD), e estresse hídrico severo, 0 a 20% (CAD). A cultivar RB72454 se mostrou a mais sensível ao déficit hídrico. Essa cultivar mostrou aumento na produção de peróxido de hidrogênio, mas sem aumento concomitante das enzimas antioxidantes ascorbato peroxidase, catalase e superóxido dismutase. Esse estresse oxidativo levou a peroxidação de lipídeos das membranas e degradação das clorofilas, resultando na diminuição da eficiência fotoquímica do PSII. Por outro lado, a cultivar RB92579 foi a mais tolerante à seca, com aumento de atividade das enzimas antioxidantes, que levou a baixa peroxidação de lipídeos, manutenção dos pigmentos fotossintéticos e da eficiência fotoquímica do PSII. O sistema de defesa antioxidante desencadeado pelas enzimas ascorbato peroxidase, catalase e superóxido dismutase parece ser o fator chave de proteção à fotoinibição de plantas de cana-de-açúcar sob estresse hídrico. O aumento do sistema antioxidante, bem como a manutenção dos pigmentos fotossintéticos e das membranas celulares serviram como critérios importantes para indicar cultivares mais tolerantes ao estresse hídrico.

Validation of reference genes for accurate normalization by quantitative polymerase chain reaction in sugarcane drought stress studies using two cultivars / Validação de genes de referência para normalização de reação em cadeia de polimerase quantitativa em estudos de estresse hídricoem cana-de-açúcar

ABSTRACT: The aim of this study was to analyze the expression of putative reference genes in sugarcane under drought stress. The varieties RB72454 and RB72910 were cultivated and the treatments control and drought stress applied to 135-day-old plants grown under field conditions. The stress level of the plants was measured by rate of photosynthesis, transpiration, and stomatal conductance. For each biological replicate, expression analyses were conducted using quantitative polymerase chain reaction for the genes α-tubulin, β-tubulin, β-actin, cyclophilin, eukaryotic elongation factor 1, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), histone H3 and ubiquitin. Stability was evaluated using the geNorm, NormFinder, and BestKeeper software packages. Among the candidate genes, GAPDH was identified as the most stable in all software, indicating its suitability for gene expression studies in sugarcane undergoing drought stress; the gene β-actin was the second most stable. These findings suggest using GAPDH and β-actin for normalization in relative gene expression in sugarcane.

RESUMO: O objetivo do estudo foi analisar a expressão de genes de referência em cana-de-açúcar sob estresse hídrico. As cultivares RB72454 e RB72910 foram cultivadas em campo e os tratamentos controle e estresse foram aplicados após 135 dias. O estresse das plantas foi mensurado utilizando as variáveis fisiológicas: taxa fotossintética, transpiração e condutância estomática. Para cada repetição biológica, a expressão gênica foi conduzida usando PCR tempo real para os genes α-tubulina, β-tubulina, β-actina, ciclofilina, fator 1 de alongamento eucariótico, gliceraldeído 3-fosfato desidrogenase (GAPDH), histona H3 e ubiquitina. A estabilidade dos genes foi avaliada usando os softwares geNorm,NormFinder e BestKeeper. Entre os genes candidatos, GAPDH foi identificado como o mais estável nos três métodos de análises, indicando ser estável para estudos de expressão gênica em cana-de-açúcar sob estresse hídrico; seguindo o gene β-actina como o segundo mais estável. Os resultados concluem que os genes GAPDH e β-actina são indicados para normalização em expressão gênica relativa, associada com estresse hídrico em cana-de-açúcar.

Expression profiles of sugarcane under drought conditions: Variation in gene regulation.

Drought is a major factor in decreased sugarcane productivity because of the resulting morphophysiological effects that it causes. Gene expression studies that have examined the influence of water stress in sugarcane have yielded divergent results, indicating the absence of a fixed pattern of changes in gene expression. In this work, we investigated the expression profiles of 12 genes in the leaves of a drought-tolerant genotype (RB72910) of sugarcane and compared the results with those of other studies. The genotype was subjected to 80-100% water availability (control condition) and 0-20% water availability (simulated drought). To analyze the physiological status, the SPAD index, Fv/Fm ratio, net photosynthesis (A), stomatal conductance (gs) and stomatal transpiration (E) were measured. Total RNA was extracted from leaves and the expression of SAMDC, ZmPIP2-1 protein, ZmTIP4-2 protein, WIP protein, LTP protein, histone H3, DNAj, ferredoxin I, ß-tubulin, photosystem I, gene 1 and gene 2 was analyzed by quantitative real-time PCR (RT-PCR). Important differences in the expression profiles of these genes were observed when compared with other genotypes, suggesting that complex defense mechanisms are activated in response to water stress. However, there was no recognizable pattern for the changes in expression of the different proteins associated with tolerance to drought stress.