Jens Sommer-Knudsen

Hydroxyproline-rich plant glycoproteins

This review summarizes the structures of the four major groups of hydroxyproline-rich glycoproteins from plants; extensins, proline/hydroxyproline-rich glycoproteins, arabinogalactan-proteins, and solanaceous lectins. Similarities and differences within and between the groups are discussed.

Proline- and hydroxyproline-rich gene products in the sexual tissues of flowers

Abstract This review summarises information on hydroxyproline-rich glycoproteins (HRGPs) and clones encoding these molecules isolated from male and female tissues of flowering plants. HRGPs are abundant in sexual tissues and a number of different HRGPs have been isolated. The protein and carbohydrate components of these HRGPs have been characterised and cDNAs encoding the protein backbones of several have been isolated and sequenced. Further work is directed at detailed structural analysis of the carbohydrate side chains of these molecules and their points of linkage to the protein backbones. The biological functions of most of these molecules have not yet been established unequivocally.

A putative O-methyltransferase from barley is induced by fungal pathogens and UV light

A cDNA clone, pBH72-F1 (F1), was isolated from a cDNA library prepared from barley leaves 72 h after inoculation with Erysiphe graminis f.sp. hordei. The 1388 bp nucleotide sequence of pBH72-F1 contains an open reading frame encoding a 42.3 kDa polypeptide of 390 amino acids which shows sequence similarity to O-methyltransferases (OMTs) from different plant species; the highest identity (41%) was observed with a putative OMT expressed in roots of maize. A phylogenetic analysis shows that the barley and maize sequences are distinctly different from the ortho-diphenol-OMTs involved in lignin formation. A putative S-adenosyl-L-methionine-binding motif (KELVDDSITN) determined for a rabbit protein-carboxyl OMT is partially conserved in the encoded amino acid sequence. Genomic Southern blot hybridization shows that pBH72-F1 probably represents a single copy gene. The F1 clone corresponds to a gene transcript exhibiting a relatively late accumulation in mildew-infected barley leaves compared to other pathogen-induced transcripts, such as transcripts encoding PR proteins, a peroxidase, and transcripts homologous to a maize caffeic acid OMT. No transcript was detected in plants exhibiting papilla resistance at time points when resistance is thought to be manifested. The atypical transcript accumulation pattern for F1 was also observed after infection by other pathogens and after UV-light treatment.

Structural Classes of Arabinogalactan-Proteins

Any consideration of the structural classes of arabinogalactan-proteins (AGPs) also raises the question, “What is an AGP?” The AGPs belong to the Hyp-rich glycoprotein (HRGP) family of molecules that also includes the extensins, Pro/Hyp-rich glycoproteins (P/HRGPs) and the solanaceous lectins (Showalter 1993, Kieliszewski and Lamport 1994, Du et al 1996a, Sommer-Knudsen et al 1998). In general, three criteria have defined AGPs: the presence of arabinogalactan chains, a Hyp-rich protein backbone and the ability to bind to a class of synthetic phenylazo dyes, the β-glycosyl Yariv et al 1962, Clarke et al 1979, Fincher et al 1983). It may now be necessary to reconsider our definitions. Arabinogalactan chains are found on proteins that do not bind the Yariv reagent [e.g., AG-peptide from wheat (Fincher et al 1974) and two glycoproteins from styles (Lind et al 1994, Sommer-Knudsen et al 1996)]. Some AGPs are Hyp-deficient, and others have short oligoarabinosides previously thought to be characteristic of the extensins and solanaceous lectins (Qi et al 1991, Baldwin et al 1993). This degree of variability is similar to that observed in glycosylation and protein backbones of the animal extracellular matrix (ECM) proteoglycans (Hardingham and Fosang 1992, Verma and Davidson 1994). These general criteria easily distinguish AGPs from the extensins and solanaceous lectins, but the boundaries between AGPs and P/HRGPs are less clearly defined. This variability raises several issues: (1) Are the criteria outlined above sufficient? (2) The AGPs are a family of molecules with different protein backbones, each existing as multiple glycoforms. Is there a distinct boundary between AGPs and P/HRGPs, or is the HRGP family a continuum of molecules? (3) Can the knowledge and experiences from the animal proteoglycan field provide additional criteria that would clarify our definitions?

Micropropagation of the nickel hyperaccumulator, Hybanthus floribundus (Family Violaceae)

A protocol for micropropagation of the nickel hyperaccumulator Hybanthus floribundus (Lindley) F. Muell. (Shrub Violet) is described in this paper. Healthy callus was first produced from stem and leaf explants on a medium containing half strength Murashige and Skoog medium with 5 μM N6-benzylaminopurine (BA) and 0.5 μM α-naphthaleneacetic acid (NAA). Numerous shoots (>20 shoots per callus) were also successfully grown from callus on this medium. The exposure time of shoots to auxin was critical for successful in vitro rooting. Best rooting efficiency was obtained by transferring shoots to auxin medium (100 μM indole-3-butyric acid) for 24 h and then to a medium without growth regulators (about 75% of treated shoots produced healthy roots). Importantly, cloned shoots retained their ability to hyperaccumulate nickel.

A micro-scale method for determining relative metal-binding affinities of proteins

This article describes a quick and easy method for determining relative binding affinities between proteins and metal ions. The method is based on separating unbound metal ions from metal ions bound to protein by ultrafiltration using microcentrifuge ultrafiltration units. Bovine serum albumin (BSA) was used as the test protein and the relative affinity towards divalent metal ions was found to be Cu2+>Zn2+>Cd2+>Pb2+>Ni2+>Co2+, which corresponds to the relative orders reported in the literature.

Arabinogalactan-Proteins in Reproductive Tissues of Flowering Plants

This paper is intended to give a historical account of the work on arabinogalactan-proteins (AGPs) that came from our research group between 1975 and 1998. Although some work of others is mentioned, the paper is not a comprehensive review. For a more extensive discussion of the subject, the reader is referred to Clarke et al (1979), Fincher et al (1983), Knox (1995), Du et al (1996a), Nothnagel (1997), Sommer-Knudsen et al (1998) and Schultz et al (1998).