Candida albicans colonization is required for invasive disease1-3. Unlike humans, adult mice with mature intact gut microbiota are resistant to C. albicans gastrointestinal (GI) colonization2,4. But the factors that promote C. albicans colonization resistance are unknown. Here we demonstrate that commensal anaerobic bacteria – specifically Clostridial Firmicutes (Clusters IV and XIVa) and Bacteroidetes – are critical for maintaining C. albicans colonization resistance in mice. Using Bacteroides thetaiotamicron as a model organism, we find that HIF-1α, a transcription factor important for activating innate immune effectors, and the antimicrobial peptide LL37-CRAMP are key determinants of C. albicans colonization resistance. While antibiotic treatment enables C. albicans colonization, pharmacologic activation of colonic Hif1a induces CRAMP expression and results in a significant reduction of C. albicans GI colonization and a 50% decrease in mortality from invasive disease. In the setting of antibiotics, Hif1a and Cramp are required for B. thetaiotamicron-induced protection against CA colonization of the gut. Thus, C. albicans GI colonization modulation by activation of gut mucosal immune effectors may represent a novel therapeutic approach for preventing invasive fungal disease in humans.

Recently, RNA-guided genome editing using the type II clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (Cas) system has been applied to edit the plant genome in several herbaceous plant species. However, it remains unknown whether this system can be used for genome editing in woody plants. In this study, we describe the genome editing and targeted gene mutation in a woody species, Populus tomentosa Carr. via the CRISPR/Cas9 system. Four guide RNAs (gRNAs) were designed to target with distinct poplar genomic sites of the phytoene desaturase gene 8 (PtoPDS) which are followed by the protospacer-adjacent motif (PAM). After Agrobacterium-mediated transformation, obvious albino phenotype was observed in transgenic poplar plants. By analyzing the RNA-guided genome-editing events, 30 out of 59 PCR clones were homozygous mutants, 2 out of 59 were heterozygous mutants and the mutation efficiency at these target sites was estimated to be 51.7%. Our data demonstrate that the Cas9/sgRNA system can be exploited to precisely edit genomic sequence and effectively create knockout mutations in woody plants.

Highlight textThis study presents the genome-wide characterization of the Populus WRKY family under biotic and abiotic stresses. Overexpression of an SA-inducible gene, PtrWRKY89, enhanced resistance to pathogens in transgenic poplar.

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Proanthocyanidins (PAs) are major defense phenolic compounds in the leaves of poplar (Populus spp.) in response to abiotic and biotic stresses. Transcriptional regulation of PA biosynthetic genes by the MYB-basic helix-loop-helix (bHLH)-WD40 complexes in poplar is not still fully understood. Here, an Arabidopsis TT2-like gene MYB115 was isolated from Populus tomentosa and characterized by various molecular, genetic and biochemical approaches. MYB115 restored PA productions in the seed coat of the Arabidopsis tt2 mutant. Overexpression of MYB115 in poplar activated expression of PA biosynthetic genes, resulting in a significant increase in PA concentrations. By contrast, the CRISPR/Cas9-generated myb115 mutant exhibited reduced PA content and decreased expression of PA biosynthetic genes. MYB115 directly activated the promoters of PA-specific structural genes. MYB115 interacted with poplar TT8. Coexpression of MYB115, TT8 and poplar TTG1 significantly enhanced the expression of ANR1 and LAR3. Additionally, transgenic plants overexpressing MYB115 had increased resistance to the fungal pathogen Dothiorella gregaria, whereas myb115 mutant exhibited greater sensitivity compared with wild-type plants. Our data provide insight into the regulatory mechanisms controlling PA biosynthesis by MYB115 in poplar, which could be effectively employed for metabolic engineering of PAs to improve resistance to fungal pathogens.