Ursula A. Hurley

Arabidopsis dynamin-like protein DRP1A: a null mutant with widespread defects in endocytosis, cellulose synthesis, cytokinesis, and cell expansion

Dynamin-related proteins are large GTPases that deform and cause fission of membranes. The DRP1 family of Arabidopsis thaliana has five members of which DRP1A, DRP1C, and DRP1E are widely expressed. Likely functions of DRP1A were identified by studying rsw9, a null mutant of the Columbia ecotype that grows continuously but with altered morphology. Mutant roots and hypocotyls are short and swollen, features plausibly originating in their cellulose-deficient walls. The reduction in cellulose is specific since non-cellulosic polysaccharides in rsw9 have more arabinose, xylose, and galactose than those in wild type. Cell plates in rsw9 roots lack DRP1A but still retain DRP1E. Abnormally placed and often incomplete cell walls are preceded by abnormally curved cell plates. Notwithstanding these division abnormalities, roots and stems add new cells at wild-type rates and organ elongation slows because rsw9 cells do not grow as long as wild-type cells. Absence of DRP1A reduces endocytotic uptake of FM4-64 into the cytoplasm of root cells and the hypersensitivity of elongation and radial swelling in rsw9 to the trafficking inhibitor monensin suggests that impaired endocytosis may contribute to the development of shorter fatter roots, probably by reducing cellulose synthesis.

Methods for Studying the Plant Cytoskeleton

The cytoskeleton is composed of organized arrays of polymeric proteins of which actin and tubulin are the most abundant. The assembled proteins provide a structural framework which supports motility and imparts order and directionality to cytoplasmic processes. This subcellular order is magnified to the level of the tissue and organ by the cytoskeleton’s role in orienting cell division and cellulose deposition and hence in defining the direction in which cells, tissues and organs will expand. Cytoskeletal function has been recently reviewed (Lloyd 1987); this chapter focuses on some important methods. We describe: i) Methods of two-dimensional immunoblotting by which isoforms of actin and tubulin can be resolved and detected with commercially available antibodies. ii) Methods which use the same antibodies to localize actin and tubulin by immunofluorescence. iii) Methods by which giant algal cells can be exploited to raise monoclonal antibodies that bind to cytoskeletal components.

Myosins from angiosperms, ferns, and algae amplification of gene fragments with versatile PCR primers and detection of protein products with a monoclonal antibody to a conserved head epitope

SummaryMyosins providing the motors for the actin-based motility that occurs in diverse plants have proved difficult to study. To facilitate those studies, we describe polymerase chain reaction primers that reliably amplify part of the myosin head from diverse plants, consensus sequences that characterise the amplified product as encoding a class V or class VIII myosin, and a monoclonal antibody that recognises an epitope conserved in the head of most plant, fungal, and animal myosins. A pair of stringent oligonucleotide primers was designed that, when used in the polymerase chain reaction, amplified at least eleven different myosins from five species of angiosperms and one sequence from each of the fernAzolla and the algaeNitella andPhaeodactylum. The amplified products, comprising 126 to 135 nucleotides encoding part of the myosin head domain, can be used as myosin-specific probes to screen genomic and cDNA libraries. To identify the products of plant myosin genes, we raised a monoclonal antibody (anti-CHE) to a nine amino acid peptide matching a conserved head epitope showing not more than single amino acid substitutions in most published myosin genes. This antibody recognises rabbit skeletal myosin and multiple polypeptides of >100 kDa in four angiosperms and in the algaNitella. Relating the Mr values of immunoreactive bands inArabidopsis extracts to the predicted Mr values of the products of five myosin genes supports the view that the antibody recognises both myosins V and VIII together with the products of some as yet unsequenced genes. The previously described MB170 antibodies may, in contrast, be specific for one or more type V myosins. Together, the polymerase chain reaction primers and the antibody represent versatile tools for identifying and categorising myosins in diverse plants.

Selective extraction of Chara actin bundles: Identification of actin and two coextracting proteins

The sub-cortical actin bundles of the alga Chara corallina can be selectively extracted with a low salt solution except when cytochalasin B is present. Proteins with molecular weights of 160000, 43000 and 37000 share this extraction behaviour. While chemical cleavage of the 43000 band indicates that it is actin, the nature of the other proteins is unknown. Although the 37000 protein resembles tropomyosin in molecular weight it lacks tropomyosins distinctively large change in electrophoretic mobility in the presence of urea.