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Homeodomain-leucine zipper type I (HD-Zip I) proteins are plant-specific transcription factors associated with the regulation of growth and development in response to changes in the environment. Nicotiana attenuata NaHD20 was identified as an HD-Zip I-coding gene whose expression was induced by multiple stress-associated stimuli including drought and wounding. To study the role of NaHD20 in the integration of stress responses with changes in growth and development, its expression was silenced by virus-induced gene silencing (VIGS), and control and silenced plants were metabolically and developmentally characterized. Phytohormone profiling showed that NaHD20 plays a positive role in abscisic acid (ABA) accumulation in leaves during water stress and in the expression of some dehydration-responsive genes including ABA biosynthetic genes. Moreover, consistent with the high levels of NaHD20 expression in corollas, the emission of benzylacetone from flowers was reduced in NaHD20-silenced plants. Additionally, bolting time and the opening of the inflorescence buds was decelerated in these plants in a specific developmental stage without affecting the total number of flowers produced. Water stress potentiated these effects; however, after plants recovered from this condition, the opening of the inflorescence buds was accelerated in NaHD20-silenced plants. In summary, NaHD20 plays multiple roles in N. attenuata and among these are the coordination of responses to dehydration and its integration with changes in flower transitions. Fil: Ré, Delfina Adela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Dezar, Carlos Alberto Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina Fil: Chan, Raquel Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina Fil: Baldwin, Ian T.. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Bonaventure, Gustavo. Instituto Max Planck Institut für Chemische Okologie; Alemania

† Background and Methods Polyploidy results in genetic turmoil, much of which is associated with new phenotypes that result in speciation. Five independent lines of synthetic allotetraploid N. � obtusiata (No) were created from crosses between the diploid N. attenuata (Na )( F) and N. obtusifolia (No )( C) and the auto- tetraploids of Na (NaT) and No (NoT) were synthesized. Their genetic, genomic and phenotypic changes were then compared with those of the parental diploid species (Na and No) as well as to the natural allotetraploids, N. quadrivalvis (Nq) and N. clevelandii (Nc), which formed 1 million years ago from crosses between ancient Na and No. † Key Results DNA fingerprinting profiles (by UP-PCR) revealed that the five No lines shared similar but not identical profiles. Both synthetic and natural polyploidy showed a dosage effect on genome size (as measured in seeds); however, only Nq was associated with a genome upsizing. Phenotypic analysis revealed that at the cellular level, No lines had phenotypes intermediate of the parental phenotypes. Both allo- and autotetraploidization had a dosage effect on seed and dry biomass (except for NaT), but not on stalk height at first flower. Nc showed paternal (Na) cellular phenotypes but inherited maternal (No) biomass and seed mass, whereas Nq showed maternal (No) cellular phenotypes but inherited paternal (Na) biomass and seed mass patterns. Principal com- ponent analysis grouped Nq with No lines, due to similar seed mass, stalk height and genome size. These traits separated Nc, No and Na from Nq and No lines, whereas biomass distinguished Na from No and Nq lines, and NaT clustered closer to Nq and No lines than to Na. † Conclusions Both allo- and autotetraploidy induce considerable morphological, genetic and genomic changes, many of which are retained by at least one of the natural polyploids. It is proposed that both natural and synthetic polyploids are well suited for studying the evolution of adaptive responses.

Disruption of the FATB gene in Arabidopsis results in a two-thirds reduction in saturated fatty acids, largely palmitate, in the leaf extra-plastidic phospholipids and a reduction in the growth rate of the mutant compared to wild type (Bonaventure G, Salas JJ, Pollard MR, Ohlrogge JB [2003] Plant Cell 15: 1020–1033). In this study, we report that although fatb-ko seedlings grow more slowly than wild type, the rate of fatty acid synthesis in leaves of the mutant increases by 40%. This results in approximately the same amount of palmitate exported from the plastid as in wild type but an increase in oleate export of about 55%. To maintain constant amounts of fatty acids in leaves, thereby counterbalancing their higher rate of production, the mutant also increases its rate of fatty acid degradation. Although fatb-ko leaves have higher rates of fatty acid synthesis and turnover, the relative proportions of membrane lipids are similar to wild type. Thus, homeostatic mechanisms to preserve membrane compositions compensate for substantial changes in rates of fatty acid and glycerolipid metabolism in the mutant. Pulse-chase labeling studies show that in fatb-ko leaves there is a net increase in the synthesis of both prokaryotic and eukaryotic lipids and consequently of their turnover. The net loss of palmitate from phosphatidylcholine plus phosphatidylethanolamine is similar for wild type and mutant, suggesting that mechanisms are not present that can preferentially preserve the saturated fatty acids. In summary, the leaf cell responds to the loss of saturated fatty acid production in the fatb-ko mutant by increasing both fatty acid synthesis and degradation, but in doing so the mechanisms for increased fatty acid turnover contribute to the lowering of the percentage of saturated fatty acids found in eukaryotic lipids.

All higher plants express several different acyl carrier protein (ACP) isoforms in a tissue-specific manner. We provide evidence that expression of mRNA for the most abundant ACP isoform in Arabidopsis leaves (ACP4) is increased severalfold by light, whereas mRNA levels for ACP isoforms 2 and 3 are independent of light. The presence of GATA-like motifs in the upstream region of theAcl1.4 gene (encoding for ACP4) and the similarity in light-mediated induction to ferredoxin-A mRNA suggests a direct role of light in Acl1.4 gene activation. Polyribosomal analysis indicated that light also affects the association of ACP transcripts with polysomes, similarly to mRNAs encoding ferredoxin-A. ACP2, ACP3, and ACP4 mRNA levels were also examined in Arabidopsis cell suspension culture and were found to be differentially controlled by metabolic and/or growth derived signals. Comparison of 5′-untranslated regions (UTRs) of ACP mRNAs of diverse plant species revealed two motifs that have been conserved during evolution, a CTCCGCC box and C-T-rich sequences. Fusions of the 5′-UTR sequences of ACP1 and ACP2 to luciferase and expression in transgenic plants indicated that the ACP1 leader contributes to preferential expression in seeds, whereas the ACP2 5′-UTR favored expression in roots. The deletion of 58 bp containing the conserved motifs of the ACP1 5′-UTR resulted in 10- to 20-fold lower gene expression in leaf and seed tissues of transgenic Arabidopsis plants.