Plants possess highly sensitive perception systems by which they recognize signal compounds originating from microbes. These molecular cues play an important role in both symbiotic and pathogenic relationships. Establishment of the soybean (Glycine max)-Bradyrhizobium symbiosis is orchestrated by specific signal molecules exchanged between appropriate plant and microbe partners: flavonoids as plant-to-bacteria signals, and Nod factor as bacteria-to-plant signals. How this signaling process interacts with stress conditions (abiotic and biotic) is the subject of this thesis. The abiotic stresses were suboptimal growth temperature, low pH, and salinity. Suboptimal growth temperatures affected the ability of the microsymbiont, Bradyrhizobim japonicum, to perceive nod gene inducers (genistein) and produce Nod factor. Nod Bj-V (C18:1, MeFuc) production by B. japonicum strains 523C and USDA110 was strongly affected by suboptimal growth temperature. Nod factor production declined with temperature, from 28 to 15°C. Strain USDA110 was more affected by decreased temperature than strain 532C. Decreased Nod factor production at low temperature was due to both decreased bacterial growth and lower production efficiency (Nod factor per cell). When a 1:1 mixture of Nod factor Nod Bj-V (C18:1, MeFuc) and Nod Bj-V (Ac, C16:0, MeFuc) was applied to soybean roots, root hair deformation increased as Nod factor concentration increased under stressfully low temperature and low pH conditions. High salinity stress strongly reduced the root hair deformation caused by Nod factor, and increasing the concentrations of added Nod factor did not over come this. Exogenous application of Nod Bj-V (C18:1, MeFuc), from strain 532C, to soybean root systems under two root zone temperatures (RZTs---17 and 25°C) reduced the progression of disease (powdery mildew---Microsphaera difussa) development on soybean leaves; this effect increased with Nod factor concentration and was gr

Signaling molecules play essential roles in communication between cells. Wnt signaling molecules are critical for embryonic development of several organisms. I examined the involvement of Wnt signaling during two major developmental processes, namely embryo implantation and formation of the embryonic body axes. Using RT-PCR analysis, I showed that multiple Wnt genes are expressed in the blastocyst at the time of implantation. Moreover, expression of Wnt 11 requires both estrogen produced by the mother and the uterine environment. Using a transgenic approach, I showed that beta-catenin-regulated transcriptional activity, which is a major transducer of Wnt signaling, is activated in the uterus specifically at the site of implantation in an embryo-dependent manner. These results introduce Wnts as candidate signaling factors that may mediate the communication between the embryo and uterus that initiates implantation. / Wnt/beta-catenin signaling triggers axis formation in Xenopus and zebrafish embryos. I showed that, during embryonic development, beta-catenin-regulated transcriptional activity is first detected in the prospective primitive streak region prior to gastrulation. This demarcates the posterior region of the embryo. This activity then becomes restricted to the elongating primitive streak and to the node. In Xenopus embryos, beta-catenin participates in the formation of the organizer through the activation of the homeodomain transcription factors Siamois and Twin. I obtained evidence that a Siamois/Twin-like binding activity exists in mouse embryos and is localized in the node. These results strongly suggest that, as the case in Xenopus and zebrafish, the Wnt/beta-catenin pathway is involved in establishing embryonic body axes. / Furthermore, using the transgenic mouse line that I generated for these studies, I mapped the transcriptional activity of beta-catenin during mouse embryonic development. These results revealed when and where this activity, and presumably Wnt signaling, is active during the development of several organs and embryonic structures.

Thesis (M.S.)--Ohio University, August, 2007. / Title from PDF t.p. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 133-173).

Thesis (Ph.D.)--Tufts University, 2000. / Adviser: Marc d'Alarcao. Submitted to the Dept. of Chemistry. Includes bibliographical references (leaves 262-271). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.)--Tufts University, 2004. / Adviser: Marc d'Alarcao. Submitted to the Dept. of Chemistry. Includes bibliographical references (leaves 114-118). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 44-52).

Thesis (Ph. D.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 214-241). Online version available on the World Wide Web.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.