Abstract Terpenes produced by plants comprise a diverse range of secondary metabolites, including volatile organic compounds (VOCs). Terpene VOC production may be altered after damage or by biological stimuli such as bacterial, fungal and insects, and subsequent triggering of plant defense responses. These VOCs originate in plants from two independent pathways: the mevalonate and the methylerythritol phosphate pathways, which utilize dimethylallyl and isopentenyl diphosphates to form the terpenoidal precursors. Phakopsora pachyrhizi fungi causes Asian soybean rust, limiting soybean production and resulting in losses of up to 80% if no control strategies are applied. By using a transcriptome datasets, we investigated the regulation of genes of the mevalonate pathway under different biotic stresses. We studied the impact of P. pachyrhizi infection in vivo expression profile of genes involved in terpenoid and glyceollin biosynthesis in genotypes harboring different resistance genes (Rpp), and across the infection cycle. In addition, we used UPLC and UPGC analysis to evaluate glyceollin and VOC production, respectively, to identify metabolites associated with soybean responses to pathogen infection. The regulation of soybean genes involved in terpene production was influenced by genotypes, depending on the Rpp gene, while glyceollin was induced in all genotypes. Furthermore, a sesquiterpene was identified as a potential marker associated with rust symptoms on soybean.

Abstract Asian soybean rust (ASR) is one of the most serious diseases for soybean crops, and it can be responsible for severe yield reduction. Due to the low durability of vertical resistance, studies on horizontal resistance are important for breeding programs. The objective of this study was to identify quantitative trait loci (QTLs) related to ASR horizontal resistance. A genetic linkage map with 26 groups was generated for simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers from 163 recombinant inbred lines (RILs). We found 13 QTLs related to 12 traits, including eight directly related to plant resistance. Furthermore, two QTLs controlling more than one trait were observed: one was related to agronomical traits, and another was related to a similar region of the Rpp3 locus associated with the number of uredinia and sporulation levels. These results will be useful for breeding programs to generate cultivars resistant to ASR.

The loss of soybean yield to Brazilian producers because of a water deficit in the 2011-2012 season was 12.9%. To reduce such losses, molecular biology techniques, including plant transformation, can be used to insert genes of interest into conventional soybean cultivars to produce lines that are more tolerant to drought. The abscisic acid (ABA)-independent Dehydration Responsive Element Binding (DREB) gene family has been used to obtain plants with increased tolerance to abiotic stresses. In the present study, the rd29A:AtDREB2A CA gene from Arabidopsis thaliana was inserted into soybean using biolistics. Seventy-eight genetically modified (GM) soybean lines containing 2-17 copies of the AtDREB2A CA gene were produced. Two GM soybean lines (P1397 and P2193) were analyzed to assess the differential expression of the AtDREB2A CA transgene in leaves and roots submitted to various dehydration treatments. Both GM lines exhibited high expression of the transgene, with the roots of P2193 showing the highest expression levels during water deficit. Physiological parameters examined during water deficit confirmed the induction of stress. This analysis of AtDREB2A CA expression in GM soybean indicated that line P2193 had the greatest stability and highest expression in roots during water deficit-induced stress.

O objetivo deste trabalho foi avaliar, por meio de enzimas marcadoras, a indução de resistência à ferrugem-asiática-da-soja em genótipos de soja contrastantes quanto à suscetibilidade a Phakopsora pachyrhizi. Aproteína total e as atividades de cinco enzimas marcadoras da indução de resistência (lipoxigenases, peroxidases, fenilalanina amônia-liase, quitinases e β-1, 3-glucanases) foram avaliadas em extratos de folhas de plantas de soja dos genótipos Embrapa 48 (suscetível) e PI 561356 (resistente), submetidas à inoculação ou não com o patógeno. Foram observadas respostas de defesa discrepantes entre os dois genótipos e entre os tempos de coleta (12, 72 e 168 horas após inoculação). A resposta de indução dessas enzimas assemelha-se à defesa bifásica, para Embrapa 48, e é consistente com o observado para outros patossistemas. No entanto, o genótipo PI 561356 respondeu com diminuição da concentração de proteína total e das atividades enzimáticas, o que indica redução do metabolismo geral das plantas infectadas. Há um importante mecanismo de resistência do genótipo PI 561356, ainda não relatado, embasado em vias que envolvem essas enzimas marcadoras e em mecanismos que utilizam menor concentração de proteínas, como os de via metabólica de resposta em cascata.

The objective of this work was to evaluate induced resistance to Asian soybean rust by means of enzyme activities in soybean genotypes contrasting as to their susceptibility to Phakopsora pachyrhizi. Total protein and the activities of five induced resistance marker enzymes (lipoxygenases, peroxidases, phenylalanine ammonia-lyase, chitinases and β-1, 3-glucanases) were evaluated in leaf extracts of soybean plants of the genotypes Embrapa 48 (susceptible) and PI 561356 (resistant), inoculated or not with the pathogen. Discrepant defense responses were obtained between the two genotypes and among the leaf harvest times (12, 72, and 168 hours after inoculation). The induction response of these enzymes resembles the biphasic defense in Embrapa 48 and is consistent with that observed in other pathological systems. However, the genotype PI 561356 responded with a decrease in total protein concentration and in enzymatic activities, indicating a general reduction in the metabolism of the infected plants. There is an important mechanism of resistance for the genotype PI 561356, not yet reported, which is grounded on the metabolic ways involving these induced resistance marker enzymes and on the mechanisms that use lower concentrations of total protein, such as the ones with metabolic pathways in response cascade.

O objetivo deste trabalho foi validar, pela técnica de PCR quantitativo em tempo real (RT-qPCR) genes para serem utilizados como referência em estudos de expressão gênica em soja, em ensaios de estresse hídrico. Foram avaliados quatro genes comumente utilizados em soja: Gmβ-actin, GmGAPDH, GmLectin e GmRNAr18S. O RNA total foi extraído de seis amostras: três amostras de raízes em sistema de hidroponia com diferentes intensidades de déficit hídrico (0, 25, 50, 75 e 100 minutos de estresse hídrico), e três amostras de folhas de plantas cultivadas em areia com diferentes umidades do solo (15, 5 e 2,5% de umidade gravimétrica). Os dados brutos do intervalo "cycle threshold" (Ct) foram analisados, e a eficiência de cada iniciador foi calculada para uma analise da Ct entre as diferentes amostras. A aplicação do programa GeNorm foi utilizada para a avaliação dos melhores genes de referência, de acordo com a estabilidade. O GmGAPDH foi o gene menos estável, com o maior valor médio de estabilidade de expressão (M), e os genes mais estáveis, com menor valor de M, foram o Gmβ-actin e GmRNAr18S, tanto nas amostras de raízes como nas de folhas. Estes genes podem ser usados em RT-qPCR como gens de referência para análises de expressão gênica.

The objective of this work was to validate, by quantitative PCR in real time (RT-qPCR), genes to be used as reference in studies of gene expression in soybean in drought-stressed trials. Four genes commonly used in soybean were evaluated: Gmβ-actin, GmGAPDH, GmLectin and GmRNAr18S. Total RNA was extracted from six samples: three from roots in a hydroponic system with different drought intensities (0, 25, 50, 75 and 100 minutes of water stress), and three from leaves of plants grown in sand with different soil moistures (15, 5 and 2.5% gravimetric humidity). The raw cycle threshold (Ct) data were analyzed, and the efficiency of each primer was calculated for an overall analysis of the Ct range among the different samples. The GeNorm application was used to evaluate the best reference gene, according to its stability. The GmGAPDH was the least stable gene, with the highest mean values of expression stability (M), and the most stable genes, with the lowest M values, were the Gmβ-actin and GmRNAr18S, when both root and leaves samples were tested. These genes can be used in RT-qPCR as reference gene for expression analysis.