Studies in Coffee

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2001. / Härtill 4 uppsatser.

Thesis (M.D.)--University of Pennsylvania, 1806. / Microform version available in the Readex Early American Imprints series.

Inaug.-Diss.--Jena.

Thèses présentées a la faculté de sciences de Paris pour obtenir le grade de docteur ès-sciences naturelles.

Thesis (M.S.)--University of Wisconsin--Madison, 1964. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 41-45.

The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, Picea abies, a representative of the gymnosperm group of seed plants. The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage. Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms. Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic Arabidopsis plants. Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns. The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.

<p>This work describes the regulation of drought stress responses in <i>Arabidopsis thaliana</i> and adresses the roles of the homeodomain-leucine zipper (HD-Zip) transcription factors in this regulation. The characteristics of <i>ATHB6</i> and <i>ATHB7</i>, two genes encoding class I HD-Zip transcription factors were analysed. </p><p>Expression of <i>ATHB6</i> and <i>ATHB7</i> was transcriptionally activated in plants subjected to water deficit or exogenous treatment with abscisic acid (ABA).</p><p>Transgenic plants constitutively expressing the <i>ATHB7</i> gene displayed a delayed elongation growth of the main inflorescence stem after transition to reproductive development. This phenotype is consistent with ATHB7 acting as a negative regulator of growth and development of the elongating stem in response to water availability.</p><p>Transgenic <i>abi1-1</i> mutant plants constitutively expressing the <i>ATHB7</i> gene displayed a reduced wiltiness as compared to monogenic <i>abi1-1</i> mutants. These data are consistent with the ATHB7 protein having a central role in the drought stress response, regulating the water balance of the plant, and acting downstream to <i>ABI1</i>. Furthermore, the data is consistent with ATHB7 acting as a positive regulator of the drought stress response.</p><p>The ABA-induced expression of the <i>ATHB7</i> gene displayed a dependence on the phytochrome system, suggesting an interplay between light and osmotic stress signaling in the regulation of the <i>ATHB7</i> gene.</p>

<p>The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, <i>Picea abies</i>, a representative of the gymnosperm group of seed plants.</p><p>The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage.</p><p>Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms.</p><p>Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic <i>Arabidopsis</i> plants.</p><p>Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns.</p><p>The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.</p>

This work describes the regulation of drought stress responses in Arabidopsis thaliana and adresses the roles of the homeodomain-leucine zipper (HD-Zip) transcription factors in this regulation. The characteristics of ATHB6 and ATHB7, two genes encoding class I HD-Zip transcription factors were analysed. Expression of ATHB6 and ATHB7 was transcriptionally activated in plants subjected to water deficit or exogenous treatment with abscisic acid (ABA). Transgenic plants constitutively expressing the ATHB7 gene displayed a delayed elongation growth of the main inflorescence stem after transition to reproductive development. This phenotype is consistent with ATHB7 acting as a negative regulator of growth and development of the elongating stem in response to water availability. Transgenic abi1-1 mutant plants constitutively expressing the ATHB7 gene displayed a reduced wiltiness as compared to monogenic abi1-1 mutants. These data are consistent with the ATHB7 protein having a central role in the drought stress response, regulating the water balance of the plant, and acting downstream to ABI1. Furthermore, the data is consistent with ATHB7 acting as a positive regulator of the drought stress response. The ABA-induced expression of the ATHB7 gene displayed a dependence on the phytochrome system, suggesting an interplay between light and osmotic stress signaling in the regulation of the ATHB7 gene.