Genetic Perturbation of the Maize Methylome

DNA methylation can play important roles in the regulation of transposable elements and genes. A collection of mutant alleles for 11 maize (Zea mays) genes predicted to play roles in controlling DNA methylation were isolated through forward- or reverse-genetic approaches. Low-coverage whole-genome bisulfite sequencing and high-coverage sequence-capture bisulfite sequencing were applied to mutant lines to determine context- and locus-specific effects of these mutations on DNA methylation profiles. Plants containing mutant alleles for components of the RNA-directed DNA methylation pathway exhibit loss of CHH methylation at many loci as well as CG and CHG methylation at a small number of loci. Plants containing loss-of-function alleles for chromomethylase (CMT) genes exhibit strong genome-wide reductions in CHG methylation and some locus-specific loss of CHH methylation. In an attempt to identify stocks with stronger reductions in DNA methylation levels than provided by single gene mutations, we performed crosses to create double mutants for the maize CMT3 orthologs, Zmet2 and Zmet5, and for the maize DDM1 orthologs, Chr101 and Chr106. While loss-of-function alleles are viable as single gene mutants, the double mutants were not recovered, suggesting that severe perturbations of the maize methylome may have stronger deleterious phenotypic effects than in Arabidopsis thaliana.     

EXTRACELLULAR INVESTMENTS IN BLUE-GREEN ALGAE WITH PARTICULAR EMPHASIS ON THE GENUS NOSTOC1

The investments of a wide variety of blue-green algae were examined. Many strains formed diffuse slime layers that were unnoticed unless mounted in India ink. Slime occurred in species with and without readily detectable sheaths. The extracellular integument type seemed consistent within strains, although the extent often varied with culture conditions. Experiments with NOSTOC on agar plates indicated that motility was inversely related to the amount of slime present. Some aspects of behavior were related to the nature of an alga's investment.     

Non-destructive estimation of lateral root distribution in an aridland perennial

Estimation of root distributions in natural systems remains challenging due to the difficulties in excavation and easy breakage of fine roots. Identifying lateral fine root distribution is necessary to determine the potential exploitation of spatially and temporally variable nutrient supplies that characterize most arid ecosystems. We estimated this potential by taking field measurements of lateral root distribution of the small herbaceous perennial Cryptantha flava (A. Nels.) Payson using ¹⁵N-enriched nutrient solutions wicked into the soil at various distances from study plants. Leaves were subsequently harvested from these plants and analyzed for N isotopic ratios. C. flava plants were capable of N uptake at distances of greater than 1.0 m from the outer edge of their aboveground canopy. The considerable lateral root neighborhood area of C. flava increases the amount of spatially variable N that is exploitable in these low-N soils. The ability to acquire spatially variable N and rapidly translate N uptake into photosynthetic carbon gain are traits that aid C. flava in maintaining its position as a successful subordinate competitor in a community dominated by larger, woody perennials.     

Helicobacter pylori: expect the unexpected

Helicobacter pylori is one of the most common bacterial infections worldwide, and virtually all infected persons develop coexisting gastritis, a signature feature of which is the capacity to persist for decades. In support of its lifestyle, H. pylori has evolved to express an array of diverse phenotypes, including enzyme functional diversity, that help to subvert obstacles presented by the human host, which permits long‐term microbial colonization. The versatility of the newly discovered enzyme LpxJ may allow H. pylori to quickly adapt to dynamic and hostile conditions present within its cognate gastric niche.