Barley (1----3,1----4)-beta-glucanase isoenzyme EI gene expression is mediated by auxin and gibberellic acid

Virus-induced gene silencing suggests (1,3;1,4)-β-glucanase is a susceptibility factor in the compatible russian wheat aphid-wheat interaction

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is a significant insect pest of wheat (Triticum aestivum L.) and has a major economic impact worldwide, especially on winter wheat in the western United States. The continuing emergence of new RWA biotypes virulent to existing resistance genes reinforces the need for more durable resistance. Studies have indicated that resistance in previously susceptible plants can be produced by knock-down of susceptibility genes or other genes involved in host plant susceptibility. Therefore, investigation into genes involved in compatible RWA-wheat interactions could be a feasible approach to achieving durable RWA resistance. The objective of this study was to test whether silencing (1,3;1,4)-β-glucanase, previously observed to be highly induced in susceptible compared with resistant wheat during aphid infestation, would confer resistance to a susceptible wheat genotype. Barley stripe mosaic virus-mediated virus-induced gene silencing was employed to test whether (1,3;1,4)-β-glucanase is involved in the susceptible reaction of 'Gamtoos-S' (GS). Controlled infestation with U.S. biotype RWA2 was done to assess aphid reproduction and host symptom development. Aphids on (1,3;1,4)-β-glucanase-silenced plants reproduced less per day and had longer prenymphipositional periods than those on control GS plants. Furthermore, the (1,3;1,4)-β-glucanase-silenced plants exhibited less chlorosis and greater dry weight compared with GS. Aphid reproduction and host plant symptom development showed linear relationships with (1,3;1,4)-β-glucanase transcript levels. Our results suggest that (1,3;1,4)-β-glucanase is required for successful infestation by the RWA and may be a susceptibility factor that could be exploited as a potential target for RWA resistance breeding.

Expression of an endo-(1,3;1,4)-beta-glucanase in response to wounding, methyl jasmonate, abscisic acid and ethephon in rice seedlings

We isolated two rice endo-(1,3;1,4)-beta-glucanase genes, denoted OsEGL1 and OsEGL2, which encoded proteins that shared 64% amino acid sequence identity. Both the OsEGL1 and OsEGL2 genes were successfully expressed in Escherichia coli to produce functional proteins. Purified OsEGL1 and OsEGL2 proteins hydrolyzed (1,3;1,4)-beta-glucans, but not (1,3;1,6)-beta-linked or (1,3)-beta-linked glucopolysaccharides nor carboxymethyl cellulose, similar to previously characterized grass endo-(1,3;1,4)-beta-glucanases. RNA blot analysis revealed that the OsEGL1 gene is expressed constitutively not only in young roots of rice seedlings, but also in mature roots of adult rice plants. Little or no expression of the OsEGL2 gene was observed in all tissues or treatments tested, but database and RT-PCR analysis indicated it is expressed in ripening panicle. In rice seedling leaves, OsEGL1 gene expression significantly increased in response to methyl jasmonate, abscisic acid, ethephon and mechanical wounding. Mechanical wounding also increased the leaf elongation rate in rice seedlings by 16% relative to that of control seedlings at day 4 after treatment. The increase in the leaf elongation rate of rice seedlings treated under mechanical wounding was concomitant with an increase in OsEGL1 expression levels in seedling leaves.

Reversible accumulation of (1-->3,1-->4)-beta-glucan endohydrolase in wheat leaves under sugar depletion

A (1-->3,1-->4)-beta-D-glucan endohydrolase [(1-->3,1-->4)-beta-glucanase, EC 3.2.1.73] was detected in wheat (Triticum aestivum L.) leaves by Western analyses and activity measurements. This enzyme is able to degrade the (1-->3,1-->4)-beta-glucans present in the cell walls of cereals and other grass species. In wheat, enzyme levels clearly increased during leaf development, reaching maximum values at full expansion and then decreasing upon leaf ageing. To test whether the abundance of (1-->3,1-->4)-beta-glucanase might be controlled by the carbohydrate status, environmental and nutritional conditions capable of altering the leaf soluble sugar contents were used. Both the activity and enzyme protein levels rapidly and markedly increased when mature leaves were depleted of sugars (e.g. during extended dark periods), whereas elevated carbohydrate contents (e.g. following continuous illumination, glucose supply in the dark or nitrogen deficiency during a light/dark cycle) caused a rapid decrease in (1-->3,1-->4)-beta-glucanase abundance or prevented its accumulation in the leaves. The physiological significance of (1-->3,1-->4)-beta-glucanase accumulation under sugar depletion remains to be elucidated.

Auxin-induced elongation growth and expressions of cell wall-bound exo- and endo-beta-glucanases in barley coleoptiles

When auxin stimulates rapid cell elongation growth of cereal coleoptiles, it causes a degradation of 1,3:1,4-beta-glucan in hemicellulosic polysaccharides. We examined gene expressions of endo-1,3:1,4-beta-glucanase (EI) and exo-beta-glucanase (ExoII), of which optimum pH are about 5, and molecular distribution of hemicellulosic polysaccharides in barley (Hordeum vulgare L.) coleoptile segments treated with or without IAA. IAA (10(-5) M) stimulated the gene expression of EI, while it did not affect that of ExoII. IAA induced gene expression of EI after 4 h and increased wall-bound glucanase activity after 8 h. The molecular weight distribution of hemicellulosic polysaccharides from coleoptile cell walls was shifted to lower molecular weight region by 2 h of IAA treatment. Fusicoccin (10(-6) M) mimicked IAA-induced elongation growth and the decrease in molecular weight of hemicellulosic 1,3:1,4-beta-glucan of coleoptiles in the first 4 h, but it did not promote elongation growth thereafter. These facts suggest that acidification of barley cell walls by IAA action enhances pre-existing cell wall-bound glucanase activity in the early first phase of IAA-induced growth and the late second phase involves the gene expression of EI by IAA.

Structure and expression of a barley acidic beta-glucanase gene

A barley acidic beta-1,3-glucanase gene was recovered from a barley genomic library by homology with a partial cDNA of barley basic beta-1,3-glucanase isoenzyme GII. The gene, Abg2, is homologous to the PR2 family of pathogenesis-related beta-1,3-glucanase genes. The ABG2 protein has 81% amino acid similarity to barley basic beta-1,3-glucanase GII. The ABG2 protein is encoded as a preprotein of 336 amino acids including a 28 amino acid signal peptide. A 299 bp intron occurs within codon 25. The mature ABG2 protein has a predicted mass of 32,642 Da and a calculated isoelectric point of 4.9. The second exon of the Abg2 gene shows a strong preference for G + C in the third position of degenerate codons. The Abg2 gene was functionally expressed in Escherichia coli. Abg2 mRNA is constitutively expressed in barley root; leaf expression of Abg2 mRNA is induced by mercuric chloride and infection by Erysiphe graminis f. sp. hordei. Southern blot analysis indicates that Abg2 is a member of a small gene family.

Differences in the thermostabilities of barley (1----3,1----4)-beta-glucanases are only partly determined by N-glycosylation

Barley (1----3,1----4)-beta-glucan 4-glucanohydrolase (EC 3.2.1.73) isoenzyme EII carries 4% by weight carbohydrate and is more stable at elevated temperatures than isoenzyme EI, which has no associated carbohydrate. The relationship between carbohydrate content and thermostability has been investigated by treatment of the two isoenzymes with N-glycopeptidase F (EC 3.5.1.52). Removal of carbohydrate from isoenzyme EII results in a decrease in the enzyme's thermostability, but treatment of isoenzyme EI with the N-glycopeptidase F has no effect. In addition, removal of a single N-glycosylation site in isoenzyme EII (Asn190-Ala-Ser) by site-directed mutagenesis of the corresponding cDNA led to a reduction in thermostability, while the introduction of this site into isoenzyme EI enhanced stability. We conclude that N-glycosylation of Asn190 enhances the stability of isoenzyme EII at elevated temperatures, but that other factors related to their primary structures also contribute to the differences in thermostabilities of the barley (1----3,1----4)-beta-glucanases.