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This study compared the transcriptional changes in Nicotiana benthamiana plants treated with homologous sequences derived from Pepper golden mosaic virus (PepGMV) and heterologous sequences that derived from another begomovirus, Tomato chino La Paz virus (ToChLPV) prior to infection by PepGMV. The results of microarray analyses identified upregulated genes associated with RNAi such as DCL2, DCL4, AGO3, AGO7, AGO10, NRPD2B (Pol IV), DRB3, CMT3, RDR6. The components that participate in different RNAi pathways were identified, including methylation induced by both constructs, as well as the code of these genes in Arabidopsis thaliana and its counterpart in N. benthamiana through different genome assembly. The expression of these genes was validated by quantitative reverse transcription polymerase chain reaction (RT-qPCR), where DCL3, DCL4, AGO1-1, AGO2, RDR6 and PPR1 showed increased expression during plant protection with the heterologous construct compared to those protected with the homologous construct. The results of this study confirmed the activation of the gene silencing mechanism at the transcriptional level with both constructs and established the possibility of their use as a protection system for both homologous and heterologous sequences., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest in the publication., (© King Abdulaziz City for Science and Technology 2021.)

This study evaluated low salinity effect on acute Hg toxicity and bioconcentration capacity in L. vannamei juveniles (8.4 ± 0.7 g), because this species is frequently exposed to hypo-osmotic environments in its natural habitat, and in farming ponds. Hg LC 50 values were 1723, 1272, 983 and 536 μg L -1 at salinity of 5 ppt (parts per thousand); 2203, 1740, 1340 and 873 μg L -1 at 10 ppt; and 7013, 5693, 1759 and 1534 μg L -1 at 25 ppt for 24, 48, 72 and 96 h, respectively. After 96 h, acute Hg toxicity in shrimp was significantly higher in salinity of 5 ppt than in 25 ppt; likewise, Hg bioconcentration in shrimp exposed to different Hg treatments was statistically greater in salinity of 5 ppt than in 25 ppt. The chemical speciation calculated in experimental waters suggested that neutral chemical Hg species (HgCl 2 and HgClOH) were the most bioavailable because their fractions (51-62%) increased when salinity decreased. Therefore, the inverse relationship between Hg toxicity and salinity was due to osmotic stress and the neutral chemical Hg species fractions that increased at lower salinities. Hg bioconcentration factors indicated that the higher Hg waterborne concentrations were the most saturated uptake and storage mechanisms in shrimp. Thus, Hg concentrations in organisms did not increase in proportion to waterborne Hg concentrations in the three salinities. These results support the hypothesis of an effect of low salinity on Hg toxicity and bioconcentration capacity in L. vannamei. The safe Hg concentrations 5.4, 8.7 and 15.3 μg L -1 were proposed for shrimp exposed to salinity of 5, 10 and 25 ppt, respectively. This information allows recognizing risky environments for both wild and cultured healthy growth of these shrimp, which can help decision makers on coastal management and shrimp pond managers to have better water quality., Competing Interests: Declaration of competing interest The authors Javier Ramírez-Rochín, Ángel I. Campa-Córdova, Martín G. Frías-Espericueta, Marcela G. Fregoso-López, Irasema E. Luis-Villaseñor and Federico Páez-Osuna of the manuscript titled “Acute mercury toxicity and bioconcentration capacity in shrimp Litopenaeus vannamei juveniles: effect of low salinity and chemical speciation” submitted to Science of the Total Environment declare the have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Biogeographic regions are defined by taxa with similar distribution patterns. Flowering plants have been widely used to propose biogeographic regionalization schemes because of shared historical or ecological factors that determine their distribution. The Mexican Transition Zone represents the boundary between the Nearctic and Neotropical kingdoms; however, there is no general agreement about the limits and extent of this region. Despite the significance of its role in the history of Mexican biota, no study involving a set of relevant plant taxa validates the magnitude of the Mexican Transition Zone. This work attempts to determine the proportion of flowering plant families and genera that characterize the biogeographic kingdoms and the Mexican Transition Zone. Through identification of distinctive genera it is shown that the Mexican Transition Zone includes the mountains of Mexico, from Oaxaca northwards. The results provide a broad view of the distribution patterns of the flora of Mexico and allow the evaluation of relationships and floristic affinities., Competing Interests: The authors have declared that no competing interests exist.

Molecular analysis of the 16S rDNA of the intestinal microbiota of whiteleg shrimp Litopenaeus vannamei was examined to investigate the effect of a Bacillus mix (Bacillus endophyticus YC3-b, Bacillus endophyticus C2-2, Bacillus tequilensisYC5-2) and the commercial probiotic (Alibio(®)) on intestinal bacterial communities and resistance to Vibrio infection. PCR and single strain conformation polymorphism (SSCP) analyses were then performed on DNA extracted directly from guts. Injection of shrimp with V. parahaemolyticus at 2.5 × 10(5) CFU g(-1) per shrimp followed 168 h after inoculation with Bacillus mix or the Alibio probiotic or the positive control. Diversity analyses showed that the bacterial community resulting from the Bacillus mix had the highest diversity and evenness and the bacterial community of the control had the lowest diversity. The bacterial community treated with probiotics mainly consisted of α- and γ-proteobacteria, fusobacteria, sphingobacteria, and flavobacteria, while the control mainly consisted of α-proteobacteria and flavobacteria. Differences were grouped using principal component analyses of PCR-SSCP of the microbiota, according to the time of inoculation. In Vibrio parahaemolyticus-infected shrimp, the Bacillus mix (~33 %) induced a significant increase in survival compared to Alibio (~21 %) and the control (~9 %). We conclude that administration of the Bacillus mix induced modulation of the intestinal microbiota of L. vannamei and increased its resistance to V. parahaemolyticus.