Publikationen - Molekulare Signalverarbeitung

A somatic embryogenesis receptor kinase like (SERKL) cDNA, designated PhSERKL, was isolated from date palm (Phoenix Dactylifera L) using RACE PCR. PhSERKL protein shared all the characteristic domains of the SERK family, including five leucine-rich repeats, one proline-rich region motif, a transmembrane domain, and kinase domains. Phylogenetic analyses using PHYLIP and Notung 2.7 programs suggest that the SERK proteins of some plant species resulted from relatively ancient duplication events. We predict an ancestor protein of monocots and dicots SERK using FASTML program. Somatic embryogenic cultures of date palm were established following transfer of callus cultures to medium containing 2, 4-dichlorophenoxyacetic acid. The role of PhSERKL gene during establishment of somatic embryogenesis in culture was investigated using quantitative real-time PCR. PhSERKL gene was highly expressed during embryogenic competence acquisition and globular embryo formation in culture. Overall, levels of expression of PhSERKL gene were lower in nonembryogenic tissues and organs than in embryogenic callus.

Coffea arabica is susceptible to several pests and diseases, some of which affect the leaves and roots. Systemic acquired resistance (SAR) is the main defence mechanism activated in plants in response to pathogen attack. Here, we report the effects of benzo(1,2,3)thiadiazole-7-carbothioic acid-s-methyl ester (BTH), a SAR chemical inducer, on the expression profile of C. arabica. Two cDNA libraries were constructed from the mRNA isolated from leaves and embryonic roots to create 1587 nonredundant expressed sequence tags (ESTs). We developed a cDNA microarray containing 1506 ESTs from the leaves and embryonic roots, and 48 NBS-LRR (nucleotide-binding site leucine-rich repeat) gene fragments derived from 2 specific genomic libraries. Competitive hybridization between untreated and BTH-treated leaves resulted in 55 genes that were significantly overexpressed and 16 genes that were significantly underexpressed. In the roots, 37 and 42 genes were over and underexpressed, respectively. A general shift in metabolism from housekeeping to defence occurred in the leaves and roots after BTH treatment. We observed a systemic increase in pathogenesis-related protein synthesis, in the oxidative burst, and in the cell wall strengthening processes. Moreover, responses in the roots and leaves varied significantly.

BackgroundCalcium signaling plays a prominent role in plants for coordinating a wide range of developmental processes and responses to environmental cues. Stimulus-specific generation of intracellular calcium transients, decoding of calcium signatures, and transformation of the signal into cellular responses are integral modules of the transduction process. Several hundred proteins with functions in calcium signaling circuits have been identified, and the number of downstream targets of calcium sensors is expected to increase. We previously identified a novel, calmodulin-binding nuclear protein, IQD1, which stimulates glucosinolate accumulation and plant defense in Arabidopsis thaliana. Here, we present a comparative genome-wide analysis of a new class of putative calmodulin target proteins in Arabidopsis and rice.ResultsWe identified and analyzed 33 and 29 IQD1-like genes in Arabidopsis thaliana and Oryza sativa, respectively. The encoded IQD proteins contain a plant-specific domain of 67 conserved amino acid residues, referred to as the IQ67 domain, which is characterized by a unique and repetitive arrangement of three different calmodulin recruitment motifs, known as the IQ, 1-5-10, and 1-8-14 motifs. We demonstrated calmodulin binding for IQD20, the smallest IQD protein in Arabidopsis, which consists of a C-terminal IQ67 domain and a short N-terminal extension. A striking feature of IQD proteins is the high isoelectric point (~10.3) and frequency of serine residues (~11%). We compared the Arabidopsis and rice IQD gene families in terms of gene structure, chromosome location, predicted protein properties and motifs, phylogenetic relationships, and evolutionary history. The existence of an IQD-like gene in bryophytes suggests that IQD proteins are an ancient family of calmodulin-binding proteins and arose during the early evolution of land plants.ConclusionComparative phylogenetic analyses indicate that the major IQD gene lineages originated before the monocot-eudicot divergence. The extant IQD loci in Arabidopsis primarily resulted from segmental duplication and reflect preferential retention of paralogous genes, which is characteristic for proteins with regulatory functions. Interaction of IQD1 and IQD20 with calmodulin and the presence of predicted calmodulin binding sites in all IQD family members suggest that IQD proteins are a new class of calmodulin targets. The basic isoelectric point of IQD proteins and their frequently predicted nuclear localization suggest that IQD proteins link calcium signaling pathways to the regulation of gene expression. Our comparative genomics analysis of IQD genes and encoded proteins in two model plant species provides the first step towards the functional dissection of this emerging family of putative calmodulin targets.

Sugarcane mosaic virus (SCMV) is an important disease in maize, which is emerging in Germany since 1983. Using this pest as a model for the inheritance of oligogenic traits, we clarified the genetic ba­sis for resistance in early maturing European maize germplasm. Screening of 122 adapted European inbred lines identified three completely resistant lines, which were used for further analyses. The genetics of SCMV resis­tance was investigated by allelism tests in field experiments combined with QTL and bulked segregant analyses (BSA) on the marker level. QTL analyses revealed the presence of two major genes Scm1 and Scm2 plus three minor QTL. Involvement of Scm1 and Scm2 in the inheritance of SCMV resistance could be confirmed by BSA in a second cross. Breeders can make use of tightly linked STS markers for marker-assisted selection (MAS) as well as our SCMV resistant flint lines to improve their elite germplasm. Currently, recurrent backcrossing with phenotypic selection is the most appropriate and cost effective breeding method. With de­creasing costs of DNA chip technology, MAS can be competitive with phenotypic selection in the near future. Further objectives of our research are the isolation and cloning of Scm1 and Scm2. To achieve this goal we follow two different approaches. (1) Positional cloning based on more than 500 AFLP primer combinations resulted in Scm1/Scm2 specific markers with a resolution of approximately 0.2 cM in the respective re­gions. (2) Resistance gene analogues (RGAs), cosegregating with the tar­get genes are used to identify further candidate genes for transformation experiments.