Genes encoding two novel members of the leucine-rich repeat receptor-like kinase (LRR-RLK) superfamily have been isolated from maize (Zea mays L.). These genes have been named ZmSERK1 and ZmSERK2 since features such as a putative leucine zipper (ZIP) and five leucine rich repeats in the extracellular domain, a proline-rich region (SPP) just upstream of the transmembrane domain and a C-terminal extension (C) after the kinase domain identify them as members of the SERK (somatic embryogenesis receptor-like kinase) family. ZmSERK1 and ZmSERK2 are single-copy genes and show 79% identity among each other in their nucleotide sequences. They share a conserved intron/exon structure with other members of the SERK family. In the maize genome, ZmSERK1 maps to position 76.9 on chromosome arm 10L and ZmSERK2 to position 143.5 on chromosome arm 5L, in regions generally not involved in duplications. ZmSERK1 is preferentially expressed in male and female reproductive tissues with strongest expression in microspores. In contrast, ZmSERK2 expression is relatively uniform in all tissues investigated. Both genes are expressed in embryogenic and non-embryogenic callus cultures.

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A reproducible transformation system for hexaploid wheat was developed based on particle bombardment of scutellar tissue of immature embryos. Particle bombardment was carried out using a PDS 1000/He gun. Plant material was bombarded with the plasmid pDB1 containing the beta-glucuronidase gene (uidA) under the control of the actin-1 promoter of rice, and the selectable marker gene bar (phosphinothricin acetyltransferase) under the control of the CaMV 35S promoter. Selection was carried out using the herbicide Basta (Glufosinate-ammonium). From a total number of 1050 bombarded immature embryos, in seven independent transformation experiments, 59 plants could be regenerated. Putative transformants were screened for enzyme activity by the histochemical GUS assay using cut leaf material and by spraying the whole plants with an aqueous solution of the herbicide Basta. Twelve regenerants survived Basta spraying and showed GUS-activity. Southern-blot analysis indicated the presence of introduced foreign genes in the genomic DNA of the transformants and both marker genes were present in all plants analysed. To date, four plants have been grown to maturity and set seed. Histochemically stained pollen grains showed a 1:1 segregation of the uidA gene in all plants tested. A 3:1 segregation of the introduced genes was demonstrated by enzyme activity tests and Southern blot analysis of R1 plants.

Pentatricopeptide repeat (PPR) proteins are members of one of the largest nucleus-encoded protein families in plants. Here, we describe the previously uncharacterized maize (Zea mays) PPR gene, MPPR6, which was isolated from a Mutator-induced collection of maize kernel mutants by a cDNA-based forward genetic approach. Identification of a second mutant allele and cosegregation analysis confirmed correlation with the mutant phenotype. Histological investigations revealed that the mutation coincides with abnormities in the transfer cell layer, retardation of embryo development, and a considerable reduction of starch level. The function of MPPR6 is conserved across a wide phylogenetic distance as revealed by heterologous complementation of the Arabidopsis thaliana mutant in the orthologous APPR6 gene. MPPR6 appeared to be exclusively present in mitochondria. RNA coimmunoprecipitation and in vitro binding studies revealed a specific physical interaction of MPPR6 with the 59 untranslated region of ribosomal protein S3 (rps3) mRNA. Mapping of transcript termini showed specifically extended rps3 59 ends in the mppr6 mutant. Considerable reduction of mitochondrial translation was observed, indicating loss of RPS3 function. This is consistent with the appearance of truncated RPS3 protein lacking the N terminus in mppr6. Our results suggest that MPPR6 is directly involved in 59 maturation and translation initiation of rps3 mRNA.

MADS box genes represent a large gene family of transcription factors with essential functions during flower development and organ differentiation processes in plants. Addressing the question of whether MADS box genes are involved in the regulation of the fertilization process and early embryo development, we have isolated two novel MADS box cDNAs, ZmMADS1 and ZmMADS3, from cDNA libraries of maize (Zea mays) pollen and egg cells, respectively. The latter gene is allelic to ZAP1. Transcripts of both genes are detectable in egg cells and in in vivo zygotes of maize. ZmMADS1 is additionally expressed in synergids and in central and antipodal cells. During early somatic embryogenesis, ZmMADS1 expression is restricted to cells with the capacity to form somatic embryos, and to globular embryos at later stages. ZmMADS3 is detectable only by more sensitive reverse transcriptase-PCR analyses, but is likewise expressed in embryogenic cultures. Both genes are not expressed in nonembryogenic suspension cultures and in isolated immature and mature zygotic embryos. During flower development, ZmMADS1 and ZmMADS3 are co-expressed in all ear spikelet organ primordia at intermediate stages. Among vegetative tissues, ZmMADS3 is expressed in stem nodes and displays a gradient with highest expression in the uppermost node. Transgenic maize plants ectopically expressing ZmMADS3 are reduced in height due to a reduced number of nodes. Reduction of seed set and male sterility were observed in the plants. The latter was due to absence of anthers. Putative functions of the genes during reproductive and vegetative developmental processes are discussed.