Celia D. Knight

Arabinogalactan Proteins Are Required for Apical Cell Extension in the Moss Physcomitrella patens

Cell biological, structural, and genetic approaches have demonstrated the presence of arabinogalactan proteins (AGPs) in the moss Physcomitrella patens and provided evidence for their function in cell expansion and specifically in the extension of apical tip-growing cells. Inhibitor studies indicated that apical cell expansion in P. patens is blocked by synthetic AGP binding β-glucosyl Yariv reagent (βGlcYR). The anti-(1→5)-α-l-arabinan monoclonal antibody LM6 binds to some AGPs in P. patens, to all plasma membranes, and to the cell wall surface at the most apical region of growing protonemal filaments. Moreover, LM6 labeling of cell walls at the tips of apical cells of P. patens was abolished in the presence of βGlcYR, suggesting that the localized movement of AGPs from the plasma membrane to the cell wall is a component of the mechanism of tip growth. Biochemical and bioinformatic analyses were used to identify seven P. patens ESTs encoding putative AGP core proteins from homology with Arabidopsis thaliana, Brassica napus, and Oryza sativa sequences and from peptide fragments isolated from βGlcYR-precipitated AGPs. Gene knockout by homologous recombination of one of these genes, P. patens AGP1, encoding a classical AGP core protein, resulted in reduced cell lengths in protonemal filaments, indicating a role for AGP1 in apical cell expansion in P. patens.

Mosses as model systems

Mosses hold many attractions as model organisms for research in plant science. Their position as the simplest of land plants makes them central to the study of plant evolution, particularly in shedding light on how their aquatic predecessors evolved to survive on land. The use of mosses for developmental studies hinges on the ability to observe development in living material at the level of the individual cell. However, more recently techniques for the molecular analysis of mosses have provided tools for new approaches for determining the mechanisms controlling plant development, incorporating both cell and molecular biology.

Molecular Responses to Abscisic Acid and Stress Are Conserved between Moss and Cereals.

Promoter elements from the wheat Em gene have been characterized. These elements are inducible by abscisic acid (ABA) and by osmotic stress. In this study, we demonstrated that the same promoter elements function in a distantly related plant species, the moss Physcomitrella patens. Transient and stable expression of the [beta]-glucuronidase reporter gene was used to determine that the heterologous wheat promoter also responds to osmotic stress and ABA in moss. Mutational analysis of the promoter indicated that the mechanism of gene regulation is conserved in both species. Gel retardation and DNase I footprint analyses were conducted to characterize further the interaction of moss transcription factors with the Em promoter. In addition, the synthesis of stress-related polypeptides in moss was observed. The evolutionary significance of these data and the potential for studying the entire ABA perception-response pathway in moss are discussed.

The Moss Physcomitrella patens, a Model System with Potential for the Study of Plant Reproduction.

The moss Physcomitrella patens has been established as a model system for the study of plant development using a combination of physiological, genetic, and molecular techniques and has been shown to be particularly suitable for the study of morphogenesis at the cellular level. Genetic and molecular techniques devised to study development include mutant isolation and analysis, somatic hybridization of sexually sterile strains, and genetic transformation. Developmental studies of Physcomitrella have so far concentrated on the early stages of gametophyte growth following spore germination or tissue regeneration. Almost no work has been done in this species on the processes involved in sexual reproduction, but it is likely that these processes would be amenable to study and that the techniques that have been devised for studying other developmental processes will also be applicable to the study of sexual reproduction. In this article, we briefly review the current state of knowledge of how development is regulated in this species, the techniques available for developmental genetic studies, and the limited amount of work that has already been done that is relevant to sexual reproduction. A recent review containing background material is given by Cove

Characterisation of Plant Exudates Inducing Chemotaxis in Nitrogen-Fixing Cyanobacteria

Cyanobacteria form symbiotic associations with a wide range of plants including cy-cads, the angiosperm Gunnera, the water fern Azolla, and bryophytes such as the liverwort Blasia and the hornwort Anthoceros (Bergman et al., 1992, 1996). The cyanobacterial symbionts in these plant symbioses are almost always members of the genus Nostoc that possess two important characteristics: they are capable of nitrogen fixation, in differentiated cells known as heterocysts (Wolk et al., 1994), and they produce specialised filaments known as hormogonia (Tandeau de Marsac, 1994). The latter are motile filaments that serve as the infective agents in most if not all the plant symbioses, and that develop from immotile parent trichomes in response to a variety of environmental stimuli (Tandeau de Marsac, 1994) including signals from potential plant hosts. For example, a hormogonia inducing factor is excreted by the hornwort Anthoceros when grown free of its symbiotic cyanobacteria in combined nitrogen-free medium (Campbell and Meeks, 1989). Similarly, the acidic mucilage secreted by Gunnera stem glands contains a hormogonia inducing activity thought to be a small, heat-labile protein (Rasmussen et al., 1994; Bergman et al., 1996). Even the roots of wheat, which forms only loose associations with cyanobacteria, release hormogonia inducing factors (Gantar et al., 1993).

Development of an electro-transformation system for Escherichia coli DH10B

Escherichia coli can be transformed to high efficiencies by subjecting a mixture of cells and DNA to a brief but intense electrical field. Factors that affect the transformation efficiency of E.coli strain DH10B were analysed. Optimal conditions gave an efficiency of 108 to 109 transformants/μg DNA with E.coli strains K803 and DH10B, and plasmids pB1221.23 and pBSK+. The use of ligated DNA resulted in 106 transformants/μg DNA. Detailed protocols for these systems are given.

Giant peroxisomes in a moss (Physcomitrella patens) peroxisomal biogenesis factor 11 mutant

Summary Peroxisomal biogenesis factor 11 (PEX11) proteins are found in yeasts, mammals and plants, and play a role in peroxisome morphology and regulation of peroxisome division. The moss Physcomitrella patens has six PEX11 isoforms which fall into two subfamilies, similar to those found in monocots and dicots. We carried out targeted gene disruption of the Phypa_PEX11‐1 gene and compared the morphological and cellular phenotypes of the wild‐type and mutant strains. The mutant grew more slowly and the development of gametophores was retarded. Mutant chloronemal filaments contained large cellular structures which excluded all other cellular organelles. Expression of fluorescent reporter proteins revealed that the mutant strain had greatly enlarged peroxisomes up to 10 μm in diameter. Expression of a vacuolar membrane marker confirmed that the enlarged structures were not vacuoles, or peroxisomes sequestered within vacuoles as a result of pexophagy. Phypa_PEX11 targeted to peroxisome membranes could rescue the knock out phenotype and interacted with Fission1 on the peroxisome membrane. Moss PEX11 functions in peroxisome division similar to PEX11 in other organisms but the mutant phenotype is more extreme and environmentally determined, making P. patens a powerful system in which to address mechanisms of peroxisome proliferation and division.

The Gatsby Plant Science Summer School: Inspiring the Next Generation of Plant Science Researchers

We provide evidence from a 5-year study to show that a single concerted effort at the start of undergraduate study can have a clear and lasting effect on the attitudes of students toward plant science. Attendance at a week-long residential plant science summer school in the first year of an undergraduate degree resulted in many students changing courses to include more plant science and increased numbers of graduates selecting plant-based PhDs. The evidence shows that the Gatsby Plant Science Summer School has increased the pool of high-quality plant science related PhD applicants in the UK and has had a positive impact on students’ career aspirations. The results are discussed within the context of enhancing the pipeline of future plant scientists and reversing the decline of this vulnerable and strategically important subject relevant to addressing food security and other major global challenges. We have shown that a single well-designed and timely intervention can influence future student behavior and as such offers a framework of potential use to other vulnerable disciplines.