Elicitor-mediated induction of chalcone isomerase in Phaseolus vulgaris cell suspension cultures

Chris Lamb: a visionary leader in plant science

Christopher John Lamb (1950-2009) made major contributions to the field of plant defense gene activation, particularly through his studies on signal transduction mechanisms. Between 1994 and 2004, he published a series of seminal papers that outlined the involvement of hydrogen peroxide, nitric oxide, lipid transfer proteins, and aspartic proteases as critical components of local and/or systemic resistance during plant-microbe interactions. Prior to this, he had been one of the first to establish the fact that induced defense responses resulted from transcriptional activation of sets of coordinately regulated genes. Chris obtained his B.S and PhD degrees in biochemistry from the University of Cambridge, United Kingdom, moving to the Botany School at the University of Oxford as a postdoctoral fellow in 1975 and to the Biochemistry Department in Oxford as a Departmental Demonstrator in 1978. He was appointed founding director of the Plant Biology Laboratory at the Salk Institute for Biological Studies in La Jolla, California in 1982, and occupied the last ten years of his life as Director of the John Innes Center, Norwich, United Kingdom. In spite of spending most of his career as a director at two of the world's most prestigious institutes, formal recognition of his achievements came late in life, with election to the Royal Society of London in 2008 and endowment of the honor of Commander of the British Empire (CBE) for his contributions to British plant science by Queen Elizabeth II in 2009. Sadly, Chris did not live to attend the official ceremony at which he would receive his CBE.

Effect of a novel chemical mixture on senescence processes and plant--fungus interaction in Solanaceae plants

The effects of exogenous application of a chemical mixture consisting of adipic acid monoethyl ester, furfurylamine, and 1,2,3,4-tetra-O-acetyl-beta-D-glucopyranose (FGA) on various metabolic pathways and the plant-fungus interaction have been studied in Solanaceae plants. Tomato and pepper plants were sprayed with the FGA mixture, and different biochemical parameters such as gas exchange, chlorophyll concentration, protein, cell wall sugar and phenolics contents, and peroxidase and phenylalanine ammonia lyase (PAL) activities were measured. FGA-treated plants showed, in general, an increase in cell wall sugar content and decreases in the chlorophyll degrading rate and the peroxidase activity. These results suggest that FGA (a possible synthetic regulator) could act as a retardant--antisenescence agent in Solanaceae plants. The FGA mixture increased the PAL activity and promoted an overall rise in the concentration of flavonoids and phenolic compounds. Therefore, FGA induced the synthesis of compounds that could give protection to plants against pathogens or insects. To further verify this putative protection, several fungi were inoculated in intact plants. Exogenous FGA applications on intact plants delayed fungus-provoked lesion development. In addition, data also showed that applications of 1,2,3,4-tetra-O-acetyl-beta-D-glucopyranose inhibited fungal growth in vitro. These results confirm that FGA can activate protective mechanisms in plants upon contact with invaders such as fungi.

Rapid changes in gene expression in response to microbial elicitation

Treatment of cell suspension cultures of French bean ( Phaseolus vulgaris ) with polysaccharide elicitor molecules from cell walls of the anthracnose fungus, Colletotrichum lindemuthianum , results in the rapid accumulation of isoflavonoid phytoalexins, deposition of wall-bound phenolic compounds and synthesis of hydroxyproline-rich glycoproteins. These changes are dependent upon a highly selective induction of gene products, including the enzymes L-phenylalanine ammonia-lyase, cytochrome P450-dependent cinnamic acid 4-hydroxylase, chalcone synthase, chalcone isomerase, prolyl hydroxylase and protein: arabinosyl transferase. Use of in vivo labelling, in vitro translation and RNA blot hybridization techniques has shown that these elicitormediated changes arise from rapid but transient induction of enzyme synthesis, resulting from the accumulation of specific mRNAs. Similar phenomena are observed in bean hypocotyls at the onset of phytoalexin synthesis in response to infection by incompatible and compatible races of C. lindemuthianum . In bean, both L-phenylalanine ammonia-lyase and chalcone synthase are encoded by multigene families and, at the protein level, both exhibit subunit and intact enzyme polymorphism. A number of less than full-length phenylalanine ammonialyase copy DNAs containing identical open reading frames have been produced from mRNA from elicitor-induced bean cells. Analysis of phenylalanine ammonia-lyase genomic clones predicts the presence of enzyme forms of differing amino acid sequence. In cultured bean cells, elicitor differentially induces the two apparent phenylalanine ammonia-lyase iso-forms with the lowest K m values. In addition to transcriptional control of the appearance of specific gene products, post-translational processes may result in increased subunit polymorphism for phenylalanine ammonia-lyase, and in the activation of chalcone isomerase. Changes in endogenous phenylpropanoid intermediate pools may signal the rapid removal of phenylalanine ammonia-lyase activity, in addition to exerting less specific inhibitory effects on the formation and/or activity of the mRNAs encoding phenylalanine ammonia-lyase and other phytoalexin biosynthetic enzymes.

The chalcone synthase multigene family of Petunia hybrida (V30): differential, light-regulated expression during flower development and UV light induction

We have analysed the expression of the 8-10 members of the gene family encoding the flavonoid biosynthetic enzyme chalcone synthase (CHS) from Petunia hybrida. During normal plant development only two members of the gene family (CHS-A and CHS-J) are expressed. Their expression is restricted to floral tissues mainly. About 90% of the total CHS mRNA pool is transcribed from CHS-A, wheares CHS-J delivers about 10% in flower corolla, tube and anthers. Expression of CHS-A and CHS-J during flower development is coordinated and (red) light-dependent. In young seedlings and cell suspension cultures expression of CHS-A and CHS-J can be induced with UV light. In addition to CHS-A and CHS-J, expression of another two CHS genes (CHS-B and CHS-G) is induced in young seedlings by UV light, albeit at a low level. In contrast to CHS genes from Leguminoseae, Petunia CHS genes are not inducible by phytopathogen-derived elicitors. Expression of CHS-A and CHS-J is reduced to a similar extent in a regulatory CHS mutant, Petunia hybrida Red Star, suggesting that both genes are regulated by the same trans-acting factors. Comparison of the promoter sequences of CHS-A and CHS-J reveals some striking homologies, which might represent cis-acting regulatory sequences.

Metabolic changes in elicitor-treated bean cells. Enzymic responses associated with rapid changes in cell wall components

Treatment of cell suspension cultures of bean (Phaseolus vulgaris c.v. Immuna) with an elicitor preparation heat-released from the cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum resulted in rapid changes in the composition of the bean cell walls. These consisted of (a) increases in phenolic material bound to the cellulosic and hemicellulosic fractions of the wall, (b) loss of material (mainly glucose) from the hemicellulosic fraction and (c) an increase in wall-associated hydroxyproline. The increases in wall-bound phenolics were preceded by (a) rapid decreases in the intracellular levels of free hydroxycinnamic acids and (b) transient increases in the extractable activities of L-phenylalanine ammonia-lyase and cinnamic acid 4-hydroxylase. 4-Hydroxycinnamic acid 3-hydroxylase activity was present at a high level in control cultures and was not induced by elicitor. Changes in the levels of cytochrome P-450, as determined by dot blot assays utilising an anti-(P-450) monoclonal antibody, paralleled the changes in cinnamic acid 4-hydroxylase activity. The accumulation of cell wall hydroxyproline was associated with rapid transient increases in the extractable activities of proline 2-oxoglutarate dioxygenase and a protein arabinosyl transferase. An hydroxyproline-rich acceptor protein of Mr 42 500 was the major protein to incorporate [3H]arabinose following elicitation of the bean cells, and the kinetics of the extent of labelling of this protein paralleled the accumulation of hydroxyproline protein in the endomembrane system. The above metabolic changes associated with cell wall components followed rapid kinetics similar to those involved in the formation of the phytoalexin kievitone in the elicited cultures [Robbins, M. P. et al. (1985) Eur. J. Biochem. 148, 563-569]. It is therefore concluded that increased 5-hydroxy-substituted isoflavonoid biosynthesis, wall-bound phenolic synthesis and synthesis of arabinosylated hydroxyproline-rich protein are all early events which are closely linked to the initial interaction between plant cell and fungal elicitor.

Induction of chalcone isomerase in elicitor-treated bean cells. Comparison of rates of synthesis and appearance of immunodetectable enzyme

Chalcone isomerase, an enzyme involved in the formation of flavonoid-derived compounds in plants, has been purified nearly 600-fold from cell suspension cultures of dwarf French bean (Phaseolus vulgaris L.). Chromatofocussing yielded a single form of the enzyme of apparent pI 5.0. This preparation was used to raise rabbit anti-(chalcone isomerase) serum. Changes in the rate of synthesis of chalcone isomerase have been investigated by indirect immunoprecipitation of enzyme labelled in vivo with [35S]methionine in elicitor-treated cultures of P. vulgaris. Elicitor, heat-released from cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes increased synthesis of the isomerase, with maximum synthetic rate occurring 11-12 h after exposure to elicitor. Immune blotting studies indicate that the elicitor-mediated increase in extractable activity of the isomerase is associated with increased appearance of immunodetactable isomerase protein of Mr 27 000. However, the maximum level of immunodetectable isomerase was attained approximately 6 h earlier than maximum extractable activity. Furthermore, a 2.8-fold increase in enzyme activity above basal levels at 12 h after elicitor-treatment was associated with a corresponding 5.8-fold increase in immunodetectable enzyme. It is concluded that elicitor induces the synthesis of both active and inactive chalcone isomerase of Mr 27 000, and that some activation of inactive enzyme occurs during the elicitor-mediated increase in isomerase activity. The presence of a pool of inactive chalcone isomerase in bean cell cultures has recently been suggested on the basis of density labelling experiments utilising 2H from 2H2O [Dixon et al. (1983) Planta (Berl.) 159, 561-569].