Cadmium and arsenic affect quiescent centre formation and maintenance in Arabidopsis thaliana post-embryonic roots disrupting auxin biosynthesis and transport

The research was focussed on the effects of cadmium (Cd) and arsenic (As), alone or combined, on Arabidopsis post-embryonic roots, with attention to quiescent centre formation and development in relation to auxin homeostasis. To the aim, morphological and histochemical analyses were carried out on seedlings, exposed or not to Cd and/or As, of wild type, and transgenic lines useful for monitoring quiescent centre identity, auxin localization and cellular influx and efflux. Moreover, auxin levels and expression of the YUC6 auxin biosynthetic gene were monitored in Cd and/or As exposed wild type seedlings. Results showed that Cd and Cd plus As increased the lateral and adventitious root density, whereas As alone reduced it. In the lateral and adventitious root apices Cd and/or As negatively affected quiescent centre identity and auxin localization, changed auxin levels, expression of YUC6, and of PIN1 and LAX3, auxin efflux and influx carriers, respectively. The alteration in auxin homeostasis was different for the two pollutants, explaining their contrasting response on the post-embryonic roots

The AtMYB11 gene from Arabidopsis is expressed in meristematic cells and modulates growth in planta and organogenesis in vitro

In plants, MYB transcription factors play important roles in many developmental processes including cell cycle progression, cell differentiation and lateral organ polarity. Here we show that the R2R3-MYB AtMYB11 gene is expressed in root and shoot meristems and also in young still meristematic leaf and flower primordia of Arabidopsis. Knock-out atmyb11-I mutants and RNAi plants germinate faster, show a faster hypocotyl and primary root elongation, develop more lateral and adventitious roots, show faster development of inflorescence, and initiate more lateral inflorescences and fruits than wild-type plants. The opposite phenotype was displayed by plants overexpressing AtMYB11. De novo formation of root meristemoids, and consequently macroscopic roots, from thin cell layers cultured in vitro was enhanced in explants from atmyb11-I and reduced in those from lines overexpressing AtMYB11. These findings indicate that AtMYB11 modulates overall growth in plants by reducing the proliferation activity of meristematic cells and delaying plant development

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century