Abscisic acid (ABA) is a phytohormone critical for plant growth, development, and adaptation to various stress conditions. Plants have to adjust ABA levels constantly to respond to changing physiological and environmental conditions. To date, the mechanisms for fine-tuning ABA levels remain elusive. Here we report that AtBG1, a beta-glucosidase, hydrolyzes glucose-conjugated, biologically inactive ABA to produce active ABA. Loss of AtBG1 causes defective stomatal movement, early germination, abiotic stress-sensitive phenotypes, and lower ABA levels, whereas plants with ectopic AtBG1 accumulate higher ABA levels and display enhanced tolerance to abiotic stress. Dehydration rapidly induces polymerization of AtBG1, resulting in a 4-fold increase in enzymatic activity. Furthermore, diurnal increases in ABA levels are attributable to polymerization-mediated AtBG1 activation. We propose that the activation of inactive ABA pools by polymerized AtBG1 is a mechanism by which plants rapidly adjust ABA levels and respond to changing environmental cues.

BackgroundSub-therapeutic antibiotics are widely used as growth promoters in the poultry industry; however, the resulting antibiotic resistance threatens public health. A plant-derived growth promoter, Macleaya cordata extract (MCE), with effective ingredients of benzylisoquinoline alkaloids, is a potential alternative to antibiotic growth promoters. Altered intestinal microbiota play important roles in growth promotion, but the underlying mechanism remains unknown.ResultsWe generated 1.64 terabases of metagenomic data from 495 chicken intestinal digesta samples and constructed a comprehensive chicken gut microbial gene catalog (9.04 million genes), which is also the first gene catalog of an animal’s gut microbiome that covers all intestinal compartments. Then, we identified the distinctive characteristics and temporal changes in the foregut and hindgut microbiota. Next, we assessed the impact of MCE on chickens and gut microbiota. Chickens fed with MCE had improved growth performance, and major microbial changes were confined to the foregut, with the predominant role of Lactobacillus being enhanced, and the amino acids, vitamins, and secondary bile acids biosynthesis pathways being upregulated, but lacked the accumulation of antibiotic-resistance genes. In comparison, treatment with chlortetracycline similarly enriched some biosynthesis pathways of nutrients in the foregut microbiota, but elicited an increase in antibiotic-producing bacteria and antibiotic-resistance genes.ConclusionThe reference gene catalog of the chicken gut microbiome is an important supplement to animal gut metagenomes. Metagenomic analysis provides insights into the growth-promoting mechanism of MCE, and underscored the importance of utilizing safe and effective growth promoters.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0590-5) contains supplementary material, which is available to authorized users.

Abscisic acid (ABA) is a stress signal, which moves in the xylem from the roots to the aerial parts of the plant, where it regulates stomatal movement and the activity of shoot meristems. Root growth-promoting microorganisms in the rhizosphere, lateral ABA flows in the root cortex across apoplastic barriers, ABA redistribution in the stem, leaf apoplastic pH values, and the action of beta-glucosidases, both in the apoplast and the cytosol of the mesophyll, play an important role in the regulation of signal intensity. The significance of abscisic acid glucose ester as a long-distance stress signal is discussed.

BackgroundThe golden apple snail (Pomacea canaliculata) is a freshwater snail listed among the top 100 worst invasive species worldwide and a noted agricultural and quarantine pest that causes great economic losses. It is characterized by fast growth, strong stress tolerance, a high reproduction rate, and adaptation to a broad range of environments.ResultsHere, we used long-read sequencing to produce a 440-Mb high-quality, chromosome-level assembly of the P. canaliculata genome. In total, 50 Mb (11.4%) repeat sequences and 21,533 gene models were identified in the genome. The major findings of this study include the recent explosion of DNA/hAT-Charlie transposable elements, the expansion of the P450 gene family, and the constitution of the cellular homeostasis system, which contributes to ecological plasticity in stress adaptation. In addition, the high transcriptional levels of perivitelline genes in the ovary and albumen gland promote the function of nutrient supply and defense ability in eggs. Furthermore, the gut metagenome also contains diverse genes for food digestion and xenobiotic degradation.ConclusionsThese findings collectively provide novel insights into the molecular mechanisms of the ecological plasticity and high invasiveness.

Mikania micrantha is one of the top 100 worst invasive species that can cause serious damage to natural ecosystems and substantial economic losses. Here, we present its 1.79 Gb chromosome-scale reference genome. Half of the genome is composed of long terminal repeat retrotransposons, 80% of which have been derived from a significant expansion in the past one million years. We identify a whole genome duplication event and recent segmental duplications, which may be responsible for its rapid environmental adaptation. Additionally, we show that M. micrantha achieves higher photosynthetic capacity by CO 2 absorption at night to supplement the carbon fixation during the day, as well as enhanced stem photosynthesis efficiency. Furthermore, the metabolites of M. micrantha can increase the availability of nitrogen by enriching the microbes that participate in nitrogen cycling pathways. These findings collectively provide insights into the rapid growth and invasive adaptation.

Using the facultative root hemiparasite Rhinanthus minor and its host Hordeum vulgare several aspects of water relations have been measured in this parasitic association. Extraction of xylem sap by the parasite from the host's roots is facilitated by con siderably higher transpiration per leaf area in the parasite than in the host and by the fact that stomata of attached Rhinanthus were open all day and night despite extremely high ABA concentrations in the leaves. By comparison, another root hemiparasite, Melampyrum arvense, parasitizing various grasses in the field, showed normal diurnal stomatal behaviour. The abnormal behaviour of Rhinanthus stomata was not due to anatomical reasons as closure could be induced by applying high external ABA concentrations. Remarkable differences have been detected between the hydraulic conductance of barley seminal roots showing relatively low values and that of Rhinanthus seminal roots showing very high values. The latter could be related to the observed high ABA concentrations in these roots. Whole plant water uptake, transpirational losses, growth-dependent deposition, and the flows of water within the plants have been measured in singly growing Rhinanthus and Hordeum plants and in the parasitic association between the two. Water uptake, deposition and transpiration in Rhinanthus were dramatically increased after attachment to the barley host; most of the water used by the parasite was extracted as xylem sap from the host, thereby scavenging 20% of the total water taken up by the host's roots. This water uptake by the parasitized host, however, due to a parasite-induced reduction in the host's growth, was decreased by 22% as compared to non-parasitized barley. The overall changes in growth-related water deposition in the host and parasite pointed to decreased shoot growth and relatively favoured root growth in the host and to strongly favoured shoot growth in the parasite. These changes in the host became more severe, when more than one Rhinanthus was parasitizing one barley plant.

Using the facultative root hemiparasite Rhinanthus minor and Hordeum vulgare as a host, the flows, depositions, and metabolism of abscisic acid (ABA) within the host, within the parasite, and between host and parasite have been studied. When the plants were supplied with 5 mM NO(3)(-), there were weak or no effects of parasitism on ABA flows, biosynthesis, and ABA degradation in barley. However, ABA deposition was significantly affected in the leaf laminae (3-fold) and in the leaf sheath (2.4-fold), but not in roots. Dramatic changes in ABA flows, metabolism, and deposition on a per plant basis, however, have been observed in Rhinanthus. Biosynthesis in the roots was 12-fold higher after attachment, resulting in 14-fold higher ABA flows in the xylem. A large portion of this ABA was metabolized, a small portion was deposited. Phloem flows of ABA were increased 13-fold after attachment. The concentrations of ABA in tissues and transport fluids were higher in attached Rhinanthus by an order of magnitude than in host tissues and xylem sap. The same tendency was also found in a comparison between single Rhinanthus and unparasitized barley. As compared with 5 mM NO(3)(-), lower NO(3)(-) or 1 mM NH(4)(+) supply doubled the ABA concentrations in barley leaf laminae, while having only small or non-significant effects in the other organs. The possible function of ABA for the parasite is discussed.

Our findings suggest that TLR/MyD88 signaling may be a therapeutic target for CAC intervention and MyD88 inhibitors may be a promising therapeutic modality for treating patients with colitis or CAC.