Transient expression of members of the germin‐like gene family in epidermal cells of wheat confers disease resistance

Abstract

The wheat genome encodes a family of germin-like proteins that differ with respect to regulation and tissue specificity of expression of the corresponding genes. While germin exhibits oxalate oxidase (E.C. 1.2.3.4.) activity, the germin-like proteins (GLPs) have no known enzymatic activity. A role of oxalate oxidase in plant defence has been proposed, based on the capacity of the enzyme to produce H2O2, a reactive oxygen species. The role in defence of germin and other members of the germin-like gene family was functionally assessed in a transient assay system based on particle bombardment of wheat leaves. Transient expression of the pathogen-induced germin gf-2.8 gene, but not of the constitutively expressed HvGLP1 gene, reduced the penetration efficiency of Blumeria (syn. Erysiphe) graminis f.sp. tritici, the causal agent of wheat powdery mildew, on transformed cells. Two engineered germin-gf-2.8 genes and the TaGLP2a gene, which all encoded proteins without oxalate oxidase activity, also reduced the penetration efficiency of the fungus, demonstrating that oxalate oxidase activity is not required for conferring enhanced resistance. Instead, activity tagging experiments showed that in cells transiently expressing the germin gf-2.8 gene, the transgene product became insolubilized at sites of attempted fungal penetration where localised production of H2O2 was observed. Thus, germin and GLPs may play a structural role in cell-wall re-enforcement during pathogen attack.

Reactive oxygen species and plant resistance to fungal pathogens

“…The family of germin-like proteins (GLP) have been associated with H 2 O 2 accumulation in infected plants (Christensen et al, 2004;Schweizer et al, 1999). GLPs include enzymes with oxalate oxidase (OxO) or superoxide dismutase (SOD) activities leading to H 2 O 2 production (Zimmermann et al, 2006).…”

Barley MLO Modulates Actin-Dependent and Actin-Independent Antifungal Defense Pathways at the Cell Periphery

“…Ballistic transformation of detached barley leaves was carried out as previously described (Schweizer et al, 1999;Elliott et al, 2005). Bombarded specimens were inoculated with high densities of powdery mildew conidiospores and GUS staining performed 48 h postinoculation (Schweizer et al, 1999).…”

“…Bombarded specimens were inoculated with high densities of powdery mildew conidiospores and GUS staining performed 48 h postinoculation (Schweizer et al, 1999). Epiphytic fungal structures were marked by Coomassie Brilliant Blue.…”

Physical and genetic mapping of barley ( Hordeum vulgare ) germin-like cDNAs

“…Elucidation of the genomic organization of the GLP family in cereals is a prerequisite for identifying the functions of the individual family members and their utilization in breeding of cereal crops. Examples of the utility of these genes are suppression of powdery mildew infection by transient expression of individual GLPs with a constitutive promoter (18) and utilization of individual GLP gene promoters for tissuespecific expression of heterologous genes (12,19). Here we present an analysis of 173 barley GLP sequences found among the nearly 50,000 sequenced and annotated barley EST clones.…”