Strigolactones (SLs), a group of carotenoid derived terpenoid lactones, are root-to-shoot phytohormones suppressing shoot branching by inhibiting the outgrowth of axillary buds. DWARF 53 (D53), the key repressor of the SL signaling pathway, is speculated to regulate the downstream transcriptional network of the SL response. However, no downstream transcription factor targeted by D53 has yet been reported. Here we report that Ideal Plant Architecture 1 (IPA1), a key regulator of the plant architecture in rice, functions as a direct downstream component of D53 in regulating tiller number and SL-induced gene expression. We showed that D53 interacts with IPA1 in vivo and in vitro and suppresses the transcriptional activation activity of IPA1. We further showed that IPA1 could directly bind to the D53 promoter and plays a critical role in the feedback regulation of SL-induced D53 expression. These findings reveal that IPA1 is likely one of the long-speculated transcription factors that act with D53 to mediate the SL-regulated tiller development in rice.

SUMMARYCucumber mosaic virus suppressor 2b (CMV2b) is a nuclear viral suppressor that interferes with local and systemic silencing and inhibits AGO1 slicer activity. CMV2b-mediated transgene hypomethylation and its localization in Cajal bodies suggests a role of CMV2b in RNA-directed DNA methylation (RdDM). However, its direct involvement in RdDM, or its binding with small RNAs (sRNAs) in vivo is not yet established. Here, we show that CMV2b binds both microRNAs (miRNAs) and small interfering RNAs (siRNAs) in vivo. sRNA sequencing data from the CMV2b immunocomplex revealed its preferential binding with 24-nt repeatassociated siRNAs. We provide evidence that CMV2b also has direct interaction with the AGO4 protein by recognizing its PAZ and PIWI domains. Subsequent analysis of AGO4 functions revealed that CMV2b reduced AGO4 slicer activity and the methylation of several loci, accompanied by the augmented accumulation of 24-nt siRNAs in Arabidopsis inflorescences. Intriguingly, CMV2b also regulated an AGO4-related epiallele independently of its catalytic potential, which further reinforces the repressive effects of CMV2b on AGO4 activity. Collectively, our results demonstrate that CMV2b can counteract AGO4-related functions. We propose that by adopting novel counter-host defense strategies against AGO1 and AGO4 proteins, CMV creates a favorable cellular niche for its proliferation.

Rice (Oryza sativa L.) is one of the world's most important staple crops and a powerful model system for studying monocot species because of its relatively small genome, rich genomic resources, and a highly efficient transformation system. With the completion of rice genome sequencing, the challenge of the post-genomic era is to systematically analyze the functions of all rice genes. Gene knockout is a frequently used and effective strategy for achieving this goal. Thus, generation of large-scale mutants at the whole-genome level is of great value for both functional genomics and genetic improvement of rice. Traditionally, large numbers of mutants are produced by physical, chemical, or biological mutagenesis. Mutants created by these methods have made enormous contributions to basic plant research and crop improvement. T-DNA insertion (Jeon et al., 2000), TILLING (targeting-induced local lesions in genomes) (Till et al., 2007) and RNAi (RNA interference) (Wang et al., 2013) are the three most common methods of performing genetic studies. T-DNA insertion and TILLING are time-consuming and labor-intensive in generating genome-wide mutant libraries, because large mutagenized populations must be generated to ensure sufficient genome-wide coverage. In addition, the T-DNA insertions occur randomly and often in intergenic and noncoding regions, for TILLING mutants it is difficult to identify the targeted mutations for the observed phenotypes, and the RNAi method only reduces the expression of targeted genes rather than generating the knockout mutants. Recently, a simple and highly efficient genomic engineering tool, the CRISPR (Clustered Regularly Interspaced Palindromic Repeats)/Cas9 system, has been developed; this technology can create small insertions and deletions (indels) in specific target genes and has been applied to many organisms. Because it is an easy and convenient technique, some CRISPR/Cas9 mutant libraries have been developed for genomewide mutation screens in cultured eukaryotic cells (Shalem et al., 2015). However, no large-scale CRISPR/Cas9 mutant libraries have yet been generated in higher plants. Here, we report the construction of a high-throughput CRISPR/Cas9 mutant library in rice and demonstrate its application for identifying gene functions and its potential use for genetic improvement.

No abstract

BackgroundRNA silencing is an important mechanism for regulation of endogenous gene expression and defense against genomic intruders in plants. This natural defense system was adopted to generate virus-resistant plants even before the mechanism of RNA silencing was unveiled. With the clarification of that mechanism, transgenic antiviral plants were developed that expressed artificial virus-specific hairpin RNAs (hpRNAs) or microRNAs (amiRNAs) in host plants. Previous works also showed that plant-mediated RNA silencing technology could be a practical method for constructing insect-resistant plants by expressing hpRNAs targeting essential genes of insects.Methodology/Principal findingsIn this study, we chose aphid Myzus persicae of order Hemiptera as a target insect. To screen for aphid genes vulnerable to attack by plant-mediated RNA silencing to establish plant aphid resistance, we selected nine genes of M. persicae as silencing targets, and constructed their hpRNA-expressing vectors. For the acetylcholinesterase 2 coding gene (MpAChE2), two amiRNA-expressing vectors were also constructed. The vectors were transformed into tobacco plants (Nicotiana tabacum cv. Xanti). Insect challenge assays showed that most of the transgenic plants gained aphid resistance, among which those expressing hpRNAs targeting V-type proton ATPase subunit E-like (V-ATPaseE) or tubulin folding cofactor D (TBCD) genes displayed stronger aphicidal activity. The transgenic plants expressing amiRNAs targeting two different sites in the MpAChE2 gene exhibited better aphid resistance than the plants expressing MpAChE2-specific hpRNA.Conclusions/SignificanceOur results indicated that plant-mediated insect-RNA silencing might be an effective way to develop plants resistant to insects with piercing-sucking mouthparts, and both the selection of vulnerable target genes and the biogenetic type of the small RNAs were crucial for the effectiveness of aphid control. The expression of insect-specific amiRNA is a promising and preferable approach to engineer plants resistant to aphids and, possibly, to other plant-infesting insects.

Background: Diabetes correlates with poor prognosis in patients with COVID-19, but very few studies have evaluated whether impaired fasting glucose (IFG) is also a risk factor for the poor outcomes of patients with COVID-19. Here we aimed to examine the associations between IFG and diabetes at admission with risks of complications and mortality among patients with COVID-19. Methods: In this multicenter retrospective cohort study, we enrolled 312 hospitalized patients with COVID-19 from 5 hospitals in Wuhan from Jan 1 to Mar 17, 2020. Clinical information, laboratory findings, complications, treatment regimens, and mortality status were collected. The associations between hyperglycemia and diabetes status at admission with primary composite end-point events (including mechanical ventilation, admission to intensive care unit, or death) were analyzed by Cox proportional hazards regression models. Results: The median age of the patients was 57 years (interquartile range 38-66), and 172 (55%) were women. At the time of hospital admission, 84 (27%) had diabetes (and 36 were new-diagnosed), 62 (20%) had IFG, and 166 (53%) had normal fasting glucose (NFG) levels. Compared to patients with NFG, patients with IFG and diabetes developed more primary composite end-point events (9 [5%], 11 [18%], 26 [31%]), including receiving mechanical ventilation (5 [3%], 6 [10%], 21 [25%]), and death (4 [2%], 9 [15%], 20 [24%]). Multivariable Cox regression analyses showed diabetes was Zhang et al. IFG and Diabetes and the Severity of COVID-19 associated increased risks of primary composite end-point events (hazard ratio 3.53; 95% confidence interval 1.48-8.40) and mortality (6.25; 1.91-20.45), and IFG was associated with an increased risk of mortality (4.11; 1.15-14.74), after adjusting for age, sex, hospitals and comorbidities. Conclusion: IFG and diabetes at admission were associated with higher risks of adverse outcomes among patients with COVID-19.

The P6 protein of Rice yellow stunt rhabdovirus (RYSV) is a virion structural protein that can be phosphorylated in vitro. However its exact function remains elusive. We found that P6 enhanced the virulence of Potato virus X (PVX) in Nicotiana benthamiana and N. tabacum plants, suggesting that it might function as a suppressor of RNA silencing. We examined the mechanism of P6-mediated silencing suppression by transiently expressing P6 in both N. benthamiana leaves and rice protoplasts. Our results showed that P6 could repress the production of secondary siRNAs and inhibit systemic green fluorescent protein RNA silencing but did not interfere with local RNA silencing in N. benthamiana plants or in rice protoplasts. Intriguingly, P6 and RDR6 had overlapping subcellular localization and P6 bound both rice and Arabidopsis RDR6 in vivo. Furthermore, transgenic rice plants expressing P6 showed enhanced susceptibility to infection by Rice stripe virus. Hence, we propose that P6 is part of the RYSV's counter-defense machinery against the plant RNA silencing system and plays a role mainly in affecting RDR6-mediated secondary siRNA synthesis. Our work provides a new perspective on how a plant-infecting nucleorhabdovirus may counteract host RNA silencing-mediated antiviral defense.

No abstract