资源环境科技发展态势分析平台

Bacteria are under immense evolutionary pressure from their viral invaders-bacteriophages. Bacteria have evolved numerous immune mechanisms, both innate and adaptive, to cope with this pressure. The discovery and exploitation of CRISPR-Cas systems have stimulated a resurgence in the identification and characterization of anti-phage mechanisms. Bacteriophages use an extensive battery of counter-defence strategies to co-exist in the presence of these diverse phage defence mechanisms. Understanding the dynamics of the interactions between these microorganisms has implications for phage-based therapies, microbial ecology and evolution, and the development of new biotechnological tools. Here we review the spectrum of anti-phage systems and highlight their evasion by bacteriophages.

CRISPR-based nucleic acid detection is used in a platform that can simultaneously detect 169 human-associated viruses in multiple samples, providing scalable, multiplexed pathogen detection aimed at routine surveillance for public health.

The great majority of globally circulating pathogens go undetected, undermining patient care and hindering outbreak preparedness and response. To enable routine surveillance and comprehensive diagnostic applications, there is a need for detection technologies that can scale to test many samples(1-3)while simultaneously testing for many pathogens(4-6). Here, we develop Combinatorial Arrayed Reactions for Multiplexed Evaluation of Nucleic acids (CARMEN), a platform for scalable, multiplexed pathogen detection. In the CARMEN platform, nanolitre droplets containing CRISPR-based nucleic acid detection reagents(7)self-organize in a microwell array(8)to pair with droplets of amplified samples, testing each sample against each CRISPR RNA (crRNA) in replicate. The combination of CARMEN and Cas13 detection (CARMEN-Cas13) enables robust testing of more than 4,500 crRNA-target pairs on a single array. Using CARMEN-Cas13, we developed a multiplexed assay that simultaneously differentiates all 169 human-associated viruses with at least 10 published genome sequences and rapidly incorporated an additional crRNA to detect the causative agent of the 2020 COVID-19 pandemic. CARMEN-Cas13 further enables comprehensive subtyping of influenza A strains and multiplexed identification of dozens of HIV drug-resistance mutations. The intrinsic multiplexing and throughput capabilities of CARMEN make it practical to scale, as miniaturization decreases reagent cost per test by more than 300-fold. Scalable, highly multiplexed CRISPR-based nucleic acid detection shifts diagnostic and surveillance efforts from targeted testing of high-priority samples to comprehensive testing of large sample sets, greatly benefiting patients and public health(9-11).

Characterization of 22-nucleotide short interfering RNAs in plants finds that they accumulate in response to environmental stress, causing translational repression, inhibition of plant growth and enhanced stress responses.

Small interfering RNAs (siRNAs) are essential for proper development and immunity in eukaryotes(1). Plants produce siRNAs with lengths of 21, 22 or 24 nucleotides. The 21- and 24-nucleotide species mediate cleavage of messenger RNAs and DNA methylation(2,3), respectively, but the biological functions of the 22-nucleotide siRNAs remain unknown. Here we report the identification and characterization of a group of endogenous 22-nucleotide siRNAs that are generated by the DICER-LIKE 2 (DCL2) protein in plants. When cytoplasmic RNA decay and DCL4 are deficient, the resulting massive accumulation of 22-nucleotide siRNAs causes pleiotropic growth disorders, including severe dwarfism, meristem defects and pigmentation. Notably, two genes that encode nitrate reductases-NIA1 and NIA2-produce nearly half of the 22-nucleotide siRNAs. Production of 22-nucleotide siRNAs triggers the amplification of gene silencing and induces translational repression both gene specifically and globally. Moreover, these 22-nucleotide siRNAs preferentially accumulate upon environmental stress, especially those siRNAs derived from NIA1/2, which act to restrain translation, inhibit plant growth and enhance stress responses. Thus, our research uncovers the unique properties of 22-nucleotide siRNAs, and reveals their importance in plant adaptation to environmental stresses.

Asteroseismology probes the internal structures of stars by using their natural pulsation frequencies(1). It relies on identifying sequences of pulsation modes that can be compared with theoretical models, which has been done successfully for many classes of pulsators, including low-mass solar-type stars(2), red giants(3), high-mass stars(4) and white dwarfs(5). However, a large group of pulsating stars of intermediate mass-the so-called delta Scuti stars-have rich pulsation spectra for which systematic mode identification has not hitherto been possible(6,7). This arises because only a seemingly random subset of possible modes are excited and because rapid rotation tends to spoil regular patterns(8-10). Here we report the detection of remarkably regular sequences of high-frequency pulsation modes in 60 intermediate-mass main-sequence stars, which enables definitive mode identification. The space motions of some of these stars indicate that they are members of known associations of young stars, as confirmed by modelling of their pulsation spectra.

The pulsation spectra of intermediate-mass stars (so-called delta Scuti stars) have been challenging to analyse, but new observations of 60 such stars reveal remarkably regular sequences of high-frequency pulsation modes.