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The LATERAL ORGAN BOUNDARIES (LOB) gene in Arabidopsis defines a new conserved protein domain. LOB is expressed in a band of cells at the adaxial base of all lateral organs formed from the shoot apical meristem and at the base of lateral roots. LOB encodes a predicted protein that does not have recognizable functional motifs, but that contains a conserved domain (the LOB domain) that is present in 42 other Arabidopsis proteins and in proteins from a variety of other plant species. Proteins showing similarity to the LOB domain were not found outside of plant databases, indicating that this unique protein may play a role in plant-specific processes. Genes encoding LOB domain proteins are expressed in a variety of temporal-and tissue-specific patterns, suggesting that they may function in diverse processes. Loss-of-function LOB mutants have no detectable phenotype under standard growth conditions, suggesting that LOB is functionally redundant or required during growth under specific environmental conditions. Ectopic expression of LOB leads to alterations in the size and shape of leaves and floral organs and causes male and female sterility. The expression of LOB at the base of lateral organs suggests a potential role for LOB in lateral organ development.The shoot apical meristem (SAM) is a group of cells at the growing tip of a plant that is formed during embryogenesis and is maintained throughout its life. The SAM is organized into a central zone composed of slowly dividing stem cells and a peripheral zone containing more rapidly dividing cells that become incorporated into organ primordia. Thus, the SAM serves as the source of cells for all initiating lateral organs of the shoot. Organs initiate in a specific pattern that depends on the positioning of founder cells in the peripheral zone. This pattern is controlled by a combination of genetic and environmental factors (Steeves and Sussex, 1989). Maintenance of the SAM requires a balance between the pool of central stem cells and the flanking peripheral zone cells. A number of genes required for SAM initiation and maintenance have been identified. Proper meristem function requires the competing action of the CLAVATA (CLV) signaling pathway and the transcription factor WUSCHEL (WUS) (for review, see Clark, 2001). The CLV pathway is required to limit the number and position of stem cells in the meristem by restricting the domain of WUS expression. In contrast, WUS is required for stem cell maintenance and is thought to act on the CLV pathway by positively regulating expression of the putative ligand encoded by CLV3. The interaction between CLV and WUS is thought to function as a feedback loop to limit meristem size (Brand et al., 2000; Schoof et al., 2000).The class 1 KNOX homeobox genes are also important for SAM function. Class 1 KNOX genes are specifically expressed in the SAM and are downregulated in lateral organ anlage in a number of plant species (Jackson et al., 1994; Long et al., 1996; Nishimura et al., 1999; Sentoku et al., 1999). Loss-offunction mutations...

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Background: Even though two prophylactic vaccines against HPV are currently licensed, infections by the virus continue to be a major health problem mainly in developing countries. The cost of the vaccines limits wide-scale application in poor countries. A promising strategy for producing affordable and efficient vaccines involves the expression of recombinant immunogens in plants. Several HPV genes have been expressed in plants, including L1, which can self-assemble into virus-like particles. A plant-based, dual prophylactic/therapeutic vaccine remains an attractive possibility.

Coordinated control of hyphal elongation and branching is essential for sustaining mycelial growth of filamentous fungi. In order to study the molecular machinery ensuring polarity control in the industrial fungus Aspergillus niger, we took advantage of the temperature-sensitive (ts) apical-branching ramosa-1 mutant. We show here that this strain serves as an excellent model system to study critical steps of polar growth control during mycelial development and report for the first time a transcriptomic fingerprint of apical branching for a filamentous fungus. This fingerprint indicates that several signal transduction pathways, including TORC2, phospholipid, calcium, and cell wall integrity signaling, concertedly act to control apical branching. We furthermore identified the genetic locus affected in the ramosa-1 mutant by complementation of the ts phenotype. Sequence analyses demonstrated that a single amino acid exchange in the RmsA protein is responsible for induced apical branching of the ramosa-1 mutant. Deletion experiments showed that the corresponding rmsA gene is essential for the growth of A. niger, and complementation analyses with Saccharomyces cerevisiae evidenced that RmsA serves as a functional equivalent of the TORC2 component Avo1p. TORC2 signaling is required for actin polarization and cell wall integrity in S. cerevisiae. Congruently, our microscopic investigations showed that polarized actin organization and chitin deposition are disturbed in the ramosa-1 mutant. The integration of the transcriptomic, genetic, and phenotypic data obtained in this study allowed us to reconstruct a model for cellular events involved in apical branching.