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PNAS Papers on Bacteria in Plants, T Helper Cell Differentiation, Superfast Bird Muscle Evolution

Researchers from Duke University and the University of Florida explore features that are shared and distinct between commensal, non-pathogenic, and pathogenic microbes living inside Arabidopsis plants. Using RNA sequencing and other approaches, the team tracked transcriptomic and population patterns for commensal bacterial species found inside Arabidopsis thaliana leaves, contrasting them with profiles for Pseudomonas syringae strains that do or do not prompt an immune response from the plants. Along with leaf gene expression profiles, the microbial findings "revealed a striking similarity between the transcriptomic features of non-pathogenic P. syringae to that of bacteria in stationary phase in vitro, a metabolically active physiological state in which the production of adaptive secondary metabolites and stress responses are induced," the authors explain, noting that a "better understanding of the nature of the long-term population dynamics and transcriptomic features associated with an endophytic commensal or pathogenic lifestyle sets a foundation for engineering of commensal microbiota or development of more effective means of pathogen population inhibition in agricultural settings."

Meanwhile, a team from the Icahn School of Medicine at Mount Sinai and Indiana University School of Medicine describes STAT3 transcription factor regulation during the differentiation of T helper 17 (Th17) cells involved in immune-related processes, including adaptive immunity. In a mouse Th17 cell model, the researchers relied on RNA sequencing, chromatin immunoprecipitation sequencing, and other methods to characterize Th17 differentiation regulators, uncovering cell type-specific STAT3 regulation by a STAT3 target: a homeodomain-interacting protein kinase 2 (Hipk2) enzyme with higher-than-usual expression in Th17 cell types. "Our study presents a previously unrecognized mechanism of self-directed cell type-specific regulation of master transcription factor Stat3 through its own transcriptional target Hipk2 in Th17 cell differentiation," they write, "and suggests a therapeutic strategy for developing a targeted therapy for Th17-associated inflammatory disorders."

Finally, investigators in the US, Sweden, and Panama consider gene expression, gene sequence, and phylogenetic features behind manakin bird radiations in Central and South America, focusing on the molecular pathways and processes that have contributed to the evolution of "superfast" muscles, which allow birds to dramatically snap their wings in mating displays. "[W]e studied the displays of manakins, who beat their wings together at nearly twice the speed of other songbirds to produce a loud 'snap' that attracts mates," the team explains, noting that the study's findings "show how innovative behavioral traits evolve as a layered process where recent molecular shift build on ancestral genetic evolutionary changes."

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