Characterization of G-Quadruplexes in Chlamydomonas reinhardtii and the Effects of Polyamine and Magnesium Cations on Structure and Stability.

Chlamydomonas reinhardtii is a green alga with a very GC-rich genome (67%) and a high density of potential G-quadruplex-forming sequences (PQSs). Using the Ensembl Plants DNA database, 19 PQSs were selected, and their ability to fold in vitro was examined using four experimental methods. Our results support in vitro folding of 18 of the 19 PQSs selected for study. The high physiological polyamine concentrations in C. reinhardtii create unique conditions for studying G4 folding. We investigated whether high polyamine concentrations affect the stability and structural fold of two polymorphic G4s selected from the cohort of PQSs. The two polymorphic G4s selected were found to be greatly stabilized when studied at the physiologically high polyamine concentrations. Lastly, the effects of physiologically relevant Mg2+ concentrations were tested on both of the polymorphic G4s, and one of the G4s shifted from a dynamic mixture of folds to favor a parallel fold in the presence of Mg2+. Our work supports the concept of folding of G4s under the unique conditions observed in C. reinhardtii, and these structures, being located in promoter regions of DNA repair and photosynthetic genes, might be relevant structures in the physiology of C. reinhardtii.

Perception of the plant hormone ethylene: known-knowns and known-unknowns.

The gaseous phytohormone ethylene is implicated in virtually all phases of plant growth and development and thus has a major impact on crop production. This agronomic impact makes understanding ethylene signaling the Philosopher's Stone of the plant biotechnology world in applications including post-harvest transport of foodstuffs, consistency of foodstuff maturity pre-harvest, decorative flower freshness and longevity, and biomass production for biofuel applications. Ethylene is biosynthesized by plants in response to environmental factors and plant life-cycle events, and triggers a signaling cascade that modulates over 1000 genes. The key components in the perception of ethylene are a family of copper dependent receptors, the bioinorganic chemistry of which has been largely ignored by the chemical community. Since identification of these receptors two decades ago, there has been tremendous growth in knowledge in the biological community on the signal transduction pathways and mechanisms of ethylene signaling. In this review, we highlight these advances and key chemical voids in knowledge that are overdue for exploration, and which are required to ultimately regulate and control ethylene signaling.