Short prokaryotic Argonaute systems trigger cell death upon detection of invading DNA.

Argonaute proteins use single-stranded RNA or DNA guides to target complementary nucleic acids. This allows eukaryotic Argonaute proteins to mediate RNA interference and long prokaryotic Argonaute proteins to interfere with invading nucleic acids. The function and mechanisms of the phylogenetically distinct short prokaryotic Argonaute proteins remain poorly understood. We demonstrate that short prokaryotic Argonaute and the associated TIR-APAZ (SPARTA) proteins form heterodimeric complexes. Upon guide RNA-mediated target DNA binding, four SPARTA heterodimers form oligomers in which TIR domain-mediated NAD(P)ase activity is unleashed. When expressed in Escherichia coli, SPARTA is activated in the presence of highly transcribed multicopy plasmid DNA, which causes cell death through NAD(P)+ depletion. This results in the removal of plasmid-invaded cells from bacterial cultures. Furthermore, we show that SPARTA can be repurposed for the programmable detection of DNA sequences. In conclusion, our work identifies SPARTA as a prokaryotic immune system that reduces cell viability upon RNA-guided detection of invading DNA.

The birth of a giant: evolutionary insights into the origin of auxin responses in plants.

The plant signaling molecule auxin is present in multiple kingdoms of life. Since its discovery, a century of research has been focused on its action as a phytohormone. In land plants, auxin regulates growth and development through transcriptional and non-transcriptional programs. Some of the molecular mechanisms underlying these responses are well understood, mainly in Arabidopsis. Recently, the availability of genomic and transcriptomic data of green lineages, together with phylogenetic inference, has provided the basis to reconstruct the evolutionary history of some components involved in auxin biology. In this review, we follow the evolutionary trajectory that allowed auxin to become the "giant" of plant biology by focusing on bryophytes and streptophyte algae. We consider auxin biosynthesis, transport, physiological, and molecular responses, as well as evidence supporting the role of auxin as a chemical messenger for communication within ecosystems. Finally, we emphasize that functional validation of predicted orthologs will shed light on the conserved properties of auxin biology among streptophytes.

Protein SUMOylation and plant abiotic stress signaling: in silico case study of rice RLKs, heat-shock and Ca(2+)-binding proteins.

Plants respond to stress conditions through early stress-response factors (ESRF), which serve the function of stress sensing and/or signal transduction. These mainly comprise qualitative and/or quantitative flux in the redox molecules, calcium ions (Ca(2+)), phosphatidic acid, hexose sugars and phytohormones. The role of resident proteins such as phytohormone receptors and G-proteins as first messengers under stress is well established. Yet, within the modern omics context, most of the stress response at the protein level is injudiciously attributed to substantial up- or down-regulation of expression measured at the RNA or protein level. Proteins such as kinases and transcription factors (TFs) that exhibit cascade effects are primary candidates for studies in plant stress tolerance. However, resident-protein post-translational modification (PTM), specifically in response to particular conditions such as stress, is a candidate for immediate and potent 'quick reaction force' (QRF) kind of effects. Stress-mediated SUMOylation of TFs and other proteins have been observed. SUMOylation can change the rate of activity, function or location of the modified protein. Early SUMOylation of resident proteins can act in the stress signal transduction or in adaptive response. Here, we consider brief background information on ESRFs to establish the crosstalk between these factors that impinge on PTMs. We then illustrate connections of protein SUMOylation to phytohormones and TFs. Finally, we present results of an in silico analysis of rice Receptor-Like Kinases, heat-shock and calcium-binding proteins to identify members of these gene families, whose basal expression under drought but potential SUMOylation presents them as QRF candidates for roles in stress signaling/response.

A long look at short prokaryotic Argonautes.

Argonaute proteins (Agos) use small 15-30 nucleotide-long guides to bind and/or cleave complementary target nucleic acids. Eukaryotic Agos mediate RNA-guided RNA silencing, while 'long' prokaryotic Agos (pAgos) use RNA or DNA guides to interfere with invading plasmid and viral DNA. Here, we review the function and mechanisms of truncated and highly divergent 'short' pAgos, which, until recently, remained functionally uncharacterized. Short pAgos have retained the Middle (MID) and P-element-Induced Wimpy Testis (PIWI) domains important for guide-mediated target binding, but lack the ability to cleave their targets. Instead, emerging insights reveal that various short pAgos interact with distinct accessory 'effector' enzymes. Upon guide-mediated detection of invading DNA by short pAgos, their associated effector enzymes kill the host cell and, consequentially, prevent spread of the invader.

Assessment of infant outgrowth of cow's milk allergy in relation to the faecal microbiome and metaproteome.

Previous studies provide evidence for an association between modifications of the gut microbiota in early life and the development of food allergies. We studied the faecal microbiota composition (16S rRNA gene amplicon sequencing) and faecal microbiome functionality (metaproteomics) in a cohort of 40 infants diagnosed with cow's milk allergy (CMA) when entering the study. Some of the infants showed outgrowth of CMA after 12 months, while others did not. Faecal microbiota composition of infants was analysed directly after CMA diagnosis (baseline) as well as 6 and 12 months after entering the study. The aim was to gain insight on gut microbiome parameters in relation to outgrowth of CMA. The results of this study show that microbiome differences related to outgrowth of CMA can be mainly identified at the taxonomic level of the 16S rRNA gene, and to a lesser extent at the protein-based microbial taxonomy and functional protein level. At the 16S rRNA gene level outgrowth of CMA is characterized by lower relative abundance of Lachnospiraceae at baseline and lower Bacteroidaceae at visit 12 months.

Design principles of a minimal auxin response system.

Auxin controls numerous growth processes in land plants through a gene expression system that modulates ARF transcription factor activity1-3. Gene duplications in families encoding auxin response components have generated tremendous complexity in most land plants, and neofunctionalization enabled various unique response outputs during development1,3,4. However, it is unclear what fundamental biochemical principles underlie this complex response system. By studying the minimal system in Marchantia polymorpha, we derive an intuitive and simple model where a single auxin-dependent A-ARF activates gene expression. It is antagonized by an auxin-independent B-ARF that represses common target genes. The expression patterns of both ARF proteins define developmental zones where auxin response is permitted, quantitatively tuned or prevented. This fundamental design probably represents the ancestral system and formed the basis for inflated, complex systems.

Anthoceros genomes illuminate the origin of land plants and the unique biology of hornworts.

Hornworts comprise a bryophyte lineage that diverged from other extant land plants >400 million years ago and bears unique biological features, including a distinct sporophyte architecture, cyanobacterial symbiosis and a pyrenoid-based carbon-concentrating mechanism (CCM). Here, we provide three high-quality genomes of Anthoceros hornworts. Phylogenomic analyses place hornworts as a sister clade to liverworts plus mosses with high support. The Anthoceros genomes lack repeat-dense centromeres as well as whole-genome duplication, and contain a limited transcription factor repertoire. Several genes involved in angiosperm meristem and stomatal function are conserved in Anthoceros and upregulated during sporophyte development, suggesting possible homologies at the genetic level. We identified candidate genes involved in cyanobacterial symbiosis and found that LCIB, a Chlamydomonas CCM gene, is present in hornworts but absent in other plant lineages, implying a possible conserved role in CCM function. We anticipate that these hornwort genomes will serve as essential references for future hornwort research and comparative studies across land plants.

Origin and evolution of the nuclear auxin response system.

The small signaling molecule auxin controls numerous developmental processes in land plants, acting mostly by regulating gene expression. Auxin response proteins are represented by large families of diverse functions, but neither their origin nor their evolution is understood. Here, we use a deep phylogenomics approach to reconstruct both the origin and the evolutionary trajectory of all nuclear auxin response protein families. We found that, while all subdomains are ancient, a complete auxin response mechanism is limited to land plants. Functional phylogenomics predicts defined steps in the evolution of response system properties, and comparative transcriptomics across six ancient lineages revealed how these innovations shaped a sophisticated response mechanism. Genetic analysis in a basal land plant revealed unexpected contributions of ancient non-canonical proteins in auxin response as well as auxin-unrelated function of core transcription factors. Our study provides a functional evolutionary framework for understanding diverse functions of the auxin signal.

Action of multiple intra-QTL genes concerted around a co-localized transcription factor underpins a large effect QTL.

Sub-QTLs and multiple intra-QTL genes are hypothesized to underpin large-effect QTLs. Known QTLs over gene families, biosynthetic pathways or certain traits represent functional gene-clusters of genes of the same gene ontology (GO). Gene-clusters containing genes of different GO have not been elaborated, except in silico as coexpressed genes within QTLs. Here we demonstrate the requirement of multiple intra-QTL genes for the full impact of QTL qDTY12.1 on rice yield under drought. Multiple evidences are presented for the need of the transcription factor 'no apical meristem' (OsNAM12.1) and its co-localized target genes of separate GO categories for qDTY12.1 function, raising a regulon-like model of genetic architecture. The molecular underpinnings of qDTY12.1 support its effectiveness in further improving a drought tolerant genotype and for its validity in multiple genotypes/ecosystems/environments. Resolving the combinatorial value of OsNAM12.1 with individual intra-QTL genes notwithstanding, identification and analyses of qDTY12.1has fast-tracked rice improvement towards food security.