The Multigene Family Encoding Germin-Like Proteins of Barley. Regulation and Function in Basal Host Resistance

Abstract

Germin-like proteins (GLPs) have been shown to be encoded by multigene families in several plant species and a role of some subfamily members in defense against pathogen attack has been proposed based on gene regulation studies and transgenic approaches. We studied the function of six GLP subfamilies of barley (Hordeum vulgare) by selecting single mRNAs for gene expression studies as well as overexpression and gene-silencing experiments in barley and Arabidopsis (Arabidopsis thaliana). Expression of all six subfamilies was high in very young seedlings, including roots. The expression pattern gradually changed from developmental to conditional with increasing plant age, whereby pathogen attack and exogenous hydrogen peroxide application were found to be the strongest signals for induction of several GLP subfamilies. Transcripts of four of five GLP subfamilies that are expressed in shoots were predominantly accumulating in the leaf epidermis. Transient overexpression of HvGER4 or HvGER5 as well as transient silencing by RNA interference of HvGER3 or HvGER5 protected barley epidermal cells from attack by the appropriate powdery mildew fungus Blumeria graminis f. sp. hordei. Silencing of HvGER4 induced hypersusceptibility. Transient and stable expression of subfamily members revealed HvGER5 as a new extracellular superoxide dismutase, and protection by overexpression could be demonstrated to be dependent on superoxide dismutase activity of the encoded protein. Data suggest a complex interplay of HvGER proteins in fine regulation of basal resistance against B. graminis.

Reactive oxygen species and plant resistance to fungal pathogens

“…An efficient way to block ROS production is difficult to find, since several major sources of ROS exist in plant cells. These include a number of enzyme systems that comprise among others NADPH oxidases, superoxide dismutase, oxalate oxidase, cell wall peroxidases, lipoxygenases and polyamine oxidases (Bolwell, 1999;Shetty et al, 2008;Torres et al, 2013;Yoda et al, 2009;Zimmermann et al, 2006). NADPH oxidases also termed homologues of mammalian respiratory burst oxidases (RBOHs) are associated with ROS formation during the interaction of plants with pathogens .…”

“…GLPs include enzymes with oxalate oxidase (OxO) or superoxide dismutase (SOD) activities leading to H 2 O 2 production (Zimmermann et al, 2006). Expression of the BvGLP-1 gene of sugar beet in Arabidopsis increased the H 2 O 2 content in the transgenic plants and conferred resistance to V. longisporum and R. solani (Knecht et al, 2010).…”

Host-Induced Gene Silencing in Barley Powdery Mildew Reveals a Class of Ribonuclease-Like Effectors

“…The resulting BEC1011-and BEC1054-wobble sequences are 61 and 67% identical to the original BEC1011 and BEC1054 sequences, respectively. These wobble sequences were subcloned into the expression vector pIPKTA9 (Zimmermann et al 2006). For each BEC, a HIGS complementation assay was then performed, in which the pIPKTA9-BEC wobble constructs were co-bombarded into barley with the corresponding RNAi silencing vector for that BEC.…”

A Germin-Like Protein Gene Family Functions as a Complex Quantitative Trait Locus Conferring Broad-Spectrum Disease Resistance in Rice

“…Oxalate oxidase-like genes, now referred to as germin-like protein (GLP) genes, belong to the functionally diverse cupin superfamily and have been identified in Arabidopsis (Arabidopsis thaliana), grapevine (Vitis vinifera), and many Gramineae species (Membre et al, 2000;Lane, 2002;Godfrey et al, 2007;Dunwell et al, 2008). Several lines of evidence suggest that GLPs are involved in general plant defense responses (Lane, 2002), including the observation that expression of certain GLPs is enhanced after infection with pathogens, feeding of insects, or application of chemicals such as salicylic acid, hydrogen peroxide (H 2 O 2 ), or ethylene (Dumas et al, 1995;Zhang et al, 1995;Wei et al, 1998;Zhou et al, 1998;Federico et al, 2006;Lou and Baldwin, 2006;Zimmermann et al, 2006;Godfrey et al, 2007). Transient overexpression of certain barley GLP subfamilies resulted in enhanced resistance to the powdery mildew fungus, and for some subfamilies, silencing resulted in enhanced susceptibility to the pathogen (Zimmermann et al, 2006).…”