The onset of leaf senescence is a highly regulated developmental change that is controlled by both genetics and the environment. Senescence is triggered by massive transcriptional reprogramming, but functional information about its underlying regulatory mechanisms is limited. In the current investigation, we performed a functional analysis of the soybean (Glycine max) osmotic stress- and endoplasmic reticulum (ER) stress-induced NAC transcription factor GmNAC81 during natural leaf senescence using overexpression studies and reverse genetics. GmNAC81-overexpressing lines displayed accelerated flowering and leaf senescence but otherwise developed normally. The precocious leaf senescence of GmNAC81-overexpressing lines was associated with greater Chl loss, faster photosynthetic decay and higher expression of hydrolytic enzyme-encoding GmNAC81 target genes, including the vacuolar processing enzyme (VPE), an executioner of vacuole-triggered programmed cell death (PCD). Conversely, virus-induced gene silencing-mediated silencing of GmNAC81 delayed leaf senescence and was associated with reductions in Chl loss, lipid peroxidation and the expression of GmNAC81 direct targets. Promoter-reporter studies revealed that the expression pattern of GmNAC81 was associated with senescence in soybean leaves. Our data indicate that GmNAC81 is a positive regulator of age-dependent senescence and may integrate osmotic stress- and ER stress-induced PCD responses with natural leaf senescence through the GmNAC81/VPE regulatory circuit.

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Molecular DNA markers are used for detection of polymorphisms in individuals. As they are independent of developmental stage of the plant and environmental influences, they can be useful tools in taxonomy. The alleles of simple sequence repeat (SSR) markers (or microsatellites) are traditionally used to identify taxonomic units. This application demands the laborious and costly delimitation of exclusive alleles in order to avoid homoplasy. Here, we propose a method for identification of species based on the amplification profile of groups of SSR markers obtained by a transferability study. The approach considers that the SSR are conserved among related species. In this context, using Psidium as a model, 141 SSR markers developed for Psidium guajava were transferred to 13 indigenous species of Psidium from the Atlantic Rainforest. Transferability of the markers was high and 28 SSR were conserved in all species. Four SSR groups were defined and they can help in the identification of all 13 Psidium species studied. A group of 31 SSR was genotyped, with one to six alleles each. The H0 varied from 0.0 to 0.46, and PIC from 0.0 to 0.74. Cluster analysis revealed shared alleles among species. The high percentage of SSR transferability found in Psidium evidences the narrow phylogenetic relationship existing among these species since transferability occurs by the preservation of the microsatellites and anchoring regions. The proposed method was useful for distinguishing the species of Psidium, being useful in taxonomic studies.

Macroscopic (germination and root growth) and microscopic (mitotic index, chromosome, and nuclear aberrations) analyses have been used to determine the toxicity of environmental pollutants. To better understand the molecular mechanisms of mutation and their effects, molecular markers offer a key perspective, as they measure the direct effects of DNA mutagenic agents. The aim of this study was to evaluate the toxic potential of the fungicides difenoconazole (DZ) and tebuconazole (TZ) on Allium cepa. A reduction was observed in the germination, root growth, and mitotic index at higher concentrations of DZ and TZ, compared to the negative control. In addition, high incidence of chromosome and nuclear aberrations was detected in treated roots. This demonstrates the genotoxic, cytotoxic, and phytotoxic effects of DZ and TZ on the root tips of A. cepa. Moreover, the molecular results indicate a change in the amplification profiles of the simple sequence repeats (SSR) and intersimple sequence repeats (ISSR) obtained from A. cepa after exposure to the tested compounds. Loss and gain of bands increased dose-dependently. Further, the grouping methods distinguished the higher concentrations from the negative control. The ISSR and SSR analyses proved to be efficient tools for evaluating DNA alterations caused by DZ and TZ. In association with macroscopic and microscopic analyses, they constitute an informative approach for environmental mutagen studies.

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The aim of this study was to evaluate the diversity of phenotypic and molecular traits in soybean cultivars launched in forty years of breeding. The DNA was amplified with 42 microsatellite markers (SSR). Polymorphisms of 38 SSR markers were identified in polyacrylamide gel at 10%. 106 alleles were amplified with an average of 2.52 alleles per SSR locus. Polymorphism information content varied from 0 to 0.68 with an average of 0.38. Genetic dissimilarities between pairs of cultivars varied from 0.4 to 0.6, 0.8 to 1.0 and 0.0 to 0.4 for data obtained from SSR markers, coefficient of parentage and phenotypic characters, respectively. It was possible to verify the contribution of cultivars considered old, intermediate and recent as well as the genetic variability of the group of cultivars used, which remained the same over 40 years of breeding. It was also observed that, with the combination of six microsatellite primers, it was possible to distinguish the 21 cultivars used in this study; and that microsatellite markers showed less biased estimates compared to the estimates obtained by the parentage coefficient and phenotypic characters in studies on genetic diversity.

O objetivo deste trabalho foi detectar e mapear locos de caracteres quantitativos (QTL) que afetam os conteúdos de proteína e óleo em soja (Glycine max L. Merr.). Plantas F2, derivadas do cruzamento entre a linhagem CS3032PTA276 e a variedade UFVS2012, foram cultivadas em casa de vegetação e forneceram as folhas para extração e análise de DNA. Quarenta e oito marcadores microssatélites (SSR) polimórficos foram avaliados na população F2. A avaliação dos fenótipos foi realizada em 207 famílias das progênies F2:3, em um delineamento em blocos ao acaso, com três repetições, conduzido em Viçosa, MG, em 2006. Foram detectados quatro QTL associados ao conteúdo de proteína, nos grupos de ligação D1a, G, A1, e I, e três QTL associados ao conteúdo de óleo, nos grupos A1, I e O. A variação fenotípica explicada pelos QTL variou de 6,24 a 18,94% e 17,26 a 25,93%, respectivamente, para os conteúdos de proteína e óleo. Foram detectados novos QTL associados aos conteúdos de proteína e óleo, além dos previamente relatados em outros estudos. Regiões distintas das atualmente conhecidas podem estar envolvidas no controle genético do teor de proteína e óleo na soja.