Publikationen - Molekulare Signalverarbeitung

Thiohydroximates comprise a diverse class of compounds important in both biological and industrial chemistry. Their syntheses are generally limited to simple alkyl and aryl compounds with few stereocenters and a narrow range of functional groups. We hypothesized that sequential action of two recombinant enzymes, a sulfatase from Helix pomatia and a β-O-glucosidase from Caldicellulosiruptor saccharolyticus, on glucosinolates would allow synthesis of thiohydroximates from a structurally broad array of abundant precursors. We report successful synthesis of thiohydroximates of varied chemical classes, including from homochiral compounds of demonstrated biological activity. The chemoenzymatic synthetic route reported here should allow access to many, if not all, of the thiohydroximate core structures of the ~200 known naturally occurring glucosinolates. The enrichment of this group for compounds with possible pharmacological potential is discussed.

Changes in root architecture are an important adaptive strategy used by plants in response to limited nutrient availability to increase the odds of acquiring them. The quiescent center (QC) plays an important role by altering the meristem activity causing differentiation and therefore, inducing a determinate growth program. The arabidopsis mutant pdr23 presents primary short root in the presence of nitrate and is inefficient in the use of nucleic acids as a source of phosphorus. In this study the effect of the pdr23 mutation on the QC maintenance under low phosphorus (P) and/or nitrogen is evaluated. QC identity is maintained in wild-type in the absence of nitrate and/or phosphate if nucleic acids can be used as an alternative source of these nutrients, but not in pdr23. The mutant is not able to use nucleic acids efficiently for substitute Pi, determinate growth is observed, similar to wild-type in the total absence of P. In the absence of N pdr23 loses the expression of QC identity marker earlier than wild-type, indicating that not only the response to P is altered, but also to N. The data suggest that the mutation affects a gene involved either in the crosstalk between these nutrients or in a pathway shared by both nutrients limitation response. Moreover loss of QC identity is also observed in wild-type in the absence of N at longer limitation. Less drastic symptoms are observed in lateral roots of both genotypes.

Phosphate (Pi) and its anhydrides constitute major nodes in metabolism. Thus, plant performance depends directly on Pi nutrition. Inadequate Pi availability in the rhizosphere is a common challenge to plants, which activate metabolic and developmental responses to maximize Pi usage and acquisition. The sensory mechanisms that monitor environmental Pi and transmit the nutritional signal to adjust root development have increasingly come into focus. Recent transcriptomic analyses and genetic approaches have highlighted complex antagonistic interactions between external Pi and Fe bioavailability and have implicated the stem cell niche as a target of Pi sensing to regulate root meristem activity.

The history of plant biology is inexorably intertwined with the conception and discovery of auxin, followed by the many decades of research to comprehend its action during growth and development. Growth responses to auxin are complex and require the coordination of auxin production, transport, and perception. In this overview of past auxin research, we limit our discourse to the mechanism of auxin action. We attempt to trace the almost epic voyage from the birth of the hormonal concept in plants to the recent crystallographic studies that resolved the TIR1-auxin receptor complex, the first structural model of a plant hormone receptor. The century-long endeavor is a beautiful illustration of the power of scientific reasoning and human intuition, but it also brings to light the fact that decisive progress is made when new technologies emerge and disciplines unite.

An improved protocol is reported to isolate and transiently transform mesophyll protoplasts of Arabidopsis thaliana. Transfected leaf protoplasts support high levels of expression of the bacterial reporter gene coding for β‐glucuronidase (GUS), under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Transient expression of GUS activity was monitored spectrophotometrically and reached a maximum between 18 and 48 h after polyethylene glycol (PEG)‐mediated DNA uptake. Histochemical staining for GUS activity revealed reproducible transformation frequencies between 40 and 60%, based on the number of protoplasts survived. To demonstrate the applicability of the transient expression system, the subcellular localization of GUS proteins tagged with different nuclear polypeptides was studied in transfected mesophyll protoplasts, revealing nuclear compartmentalization of the chimeric GUS enzymes. Furthermore, Arabidopsis mesophyll protoplasts support auxin‐mediated induction of chloramphenicol acetyl‐transferase (CAT) activity when transfected with a transcriptional fusion between the CAT reporter gene and the early auxin‐inducible PS‐IAA4/5 promoter. Hence, the method allows in vivo analysis of promoter activity and subcellular localization of fusion proteins in a homologous transformation system.

The plant growth hormone indoleacetic acid (IAA) transcriptionally activates gene expression in plants. Some of the genes whose expression is induced by IAA encode a family of proteins in pea (PS-IAA4 and PS-IAA6) and Arabidopsis (IAA1 and IAA2) that contain putative nuclear localization signals that direct a beta-glucuronidase reporter protein into the nucleus. Pulse-chase and immunoprecipitation experiments have defined the t1/2 of the PS-IAA4 and PS-IAA6 proteins to be 8 and 6 min, respectively. Their most prominent feature is the presence of a beta alpha alpha motif similar to the beta-sheet DNA-binding domain found in prokaryotic repressors of the Arc family. Based on these data, we suggest that plant tissues express short-lived nuclear proteins as a primary response to IAA. We propose that these proteins act as activators or repressors of genes responsible for mediating the various auxin responses.