A eudicot MIXTA family ancestor likely functioned in both conical cells and trichomes.

The MIXTA family of MYB transcription factors modulate the development of diverse epidermal features in land plants. This study investigates the evolutionary history and function of the MIXTA gene family in the early-diverging eudicot model lineage Thalictrum (Ranunculaceae), with R2R3 SBG9-A MYB transcription factors representative of the pre-core eudicot duplication and thus hereby referred to as "paleoMIXTA" (PMX). Cloning and phylogenetic analysis of Thalictrum paleoMIXTA (ThPMX) orthologs across 23 species reveal a genus-wide duplication coincident with a whole-genome duplication. Expression analysis by qPCR confirmed that the highest expression is found in carpels, while newly revealing high expression in leaves and nuanced differences between paralogs in representative polyploid species. The single-copy ortholog from the diploid species T. thalictroides (TthPMX, previously TtMYBML2), which has petaloid sepals with conical-papillate cells and trichomes on leaves, was functionally characterized by virus-induced gene silencing (VIGS), and its role in leaves was also assessed from heterologous overexpression in tobacco. Another ortholog from a species with conical-papillate cells on stamen filaments, TclPMX, was also targeted for silencing. Overexpression assays in tobacco provide further evidence that the paleoMIXTA lineage has the potential for leaf trichome function in a core eudicot. Transcriptome analysis by RNA-Seq on leaves of VIGS-treated plants suggests that TthPMX modulates leaf trichome development and morphogenesis through microtubule-associated mechanisms and that this may be a conserved pathway for eudicots. These experiments provide evidence for a combined role for paleoMIXTA orthologs in (leaf) trichomes and (floral) conical-papillate cells that, together with data from other systems, makes the functional reconstruction of a eudicot ancestor most likely as also having a combined function.

The impact of early-life sub-therapeutic antibiotic treatment (STAT) on excessive weight is robust despite transfer of intestinal microbes.

The high-fat, high-calorie diets of westernized cultures contribute to the global obesity epidemic, and early life exposure to antibiotics may potentiate those dietary effects. Previous experiments with mice had shown that sub-therapeutic antibiotic treatment (STAT)-even restricted to early life-affected the gut microbiota, altered host metabolism, and increased adiposity throughout the lifetime of the animals. Here we carried out a large-scale cohousing experiment to investigate whether cohousing STAT and untreated (Control) mice would transfer the STAT-perturbed microbiota and transmit its impact on weight. We exposed pregnant dams and their young offspring to either low-dose penicillin (STAT) or water (Control) until weaning, and then followed the offspring as they grew and endured a switch from normal to high-fat diet at week 17 of life. Cohousing, which started at week 4, rapidly approximated the microbiota within cages, lowering the weight of STAT mice relative to non-cohoused mice. The effect, however, varied between cages, and was restricted to the first 16 weeks when diet consisted of normal chow. Once mice switched to high-fat diet, the microbiota α- and ß-diversity expanded and the effect of cohousing faded: STAT mice, again, were heavier than control mice independently of cohousing. Metabolomics revealed serum metabolites associated with STAT exposure, but no significant differences were detected in glucose or insulin tolerance. Our results show that cohousing can partly ameliorate the impact of STAT on the gut microbiota but not prevent increased weight with high-fat diet. These observations have implications for microbiota therapies aimed to resolve the collateral damage of antibiotics and their load on human obesity.

Intergenerational transfer of antibiotic-perturbed microbiota enhances colitis in susceptible mice.

Antibiotic exposure in children has been associated with the risk of inflammatory bowel disease (IBD). Antibiotic use in children or in their pregnant mother can affect how the intestinal microbiome develops, so we asked whether the transfer of an antibiotic-perturbed microbiota from mothers to their children could affect their risk of developing IBD. Here we demonstrate that germ-free adult pregnant mice inoculated with a gut microbial community shaped by antibiotic exposure transmitted their perturbed microbiota to their offspring with high fidelity. Without any direct or continued exposure to antibiotics, this dysbiotic microbiota in the offspring remained distinct from controls for at least 21 weeks. By using both IL-10-deficient and wild-type mothers, we showed that both inoculum and genotype shape microbiota populations in the offspring. Because IL10-/- mice are genetically susceptible to colitis, we could assess the risk due to maternal transmission of an antibiotic-perturbed microbiota. We found that the IL10-/- offspring that had received the perturbed gut microbiota developed markedly increased colitis. Taken together, our findings indicate that antibiotic exposure shaping the maternal gut microbiota has effects that extend to the offspring, with both ecological and long-term disease consequences.

An ortholog of MIXTA-like2 controls epidermal cell shape in flowers of Thalictrum.

Here, we investigated the genetic underpinnings of pollination-related floral phenotypes in Thalictrum, a ranunculid with apetalous flowers. The variable presence of petaloid features in other floral organs correlates with distinct adaptations to insect vs. wind pollination. Conical cells are present in sepals or stamens of insect-pollinated species, and in stigmas. We characterized a Thalictrum ortholog of the Antirrhinum majus transcription factor MIXTA-like2, responsible for conical cells, from three species with distinct floral morphologies, representing two pollination syndromes. Genes were cloned by PCR and analysed phylogenetically. Expression analyses were conducted by quantitative PCR and in situ hybridization, followed by functional studies in transgenic tobacco. The cloned genes encode R2R3 MYB proteins closely related to Antirrhinum AmMYBML2 and Petunia hybrida PhMYB1. Spatial expression by in situ hybridization overlaps areas of conical cells. Overexpression in tobacco induces cell outgrowths in carpel epidermis and significantly increases the height of petal conical cells. We have described the first orthologs of AmMIXTA-like2 outside the core eudicots, likely ancestral to the MIXTA/MIXTA-like1 duplication. The conserved role in epidermal cell elongation results in conical cells, micromorphological markers for petaloidy. This adaptation to attract insect pollinators was apparently lost after the evolution of wind pollination in Thalictrum.