Abstract
Localized cell wall thickenings, so called papillae, are a common plant defense response to fungal attack at sites of penetration of the plant cell. The major constituent of papillae is callose, a (1,3)-β-glucan polymer, which contributes to slowing or blocking the invading fungal hyphae. In the model plant Arabidopsis thaliana, we could recently show that the overexpression of PMR4(POWDERY MILDEW RESITANT 4), which encodes a stress induced callose synthase, results in complete powdery mildew resistance. To evaluate if these findings are also transferable to monocot crops, we transiently expressed PMR4 under control of the 35S promoter in leaves of barley (Hordeum vulgare) seedlings, which were subsequently inoculated with the virulent powdery mildew Blumeria graminis f. sp. hordei. Fusion of the green fluorescent protein (GFP) to PMR4 allowed the identification of successfully transformed barley cells, which showed an increased penetration resistance to B. graminis compared to control cells that express only GFP.PMR4-GFP localized in a similar pattern at the site of attempted fungal penetration as observed inA. thaliana, which suggests that similar transport mechanisms of the callose synthase might exist in dicot and monocot plants.
Highlights
The plant cell wall is one of the first lines of defense against invading pathogens
To evaluate if these findings are transferable to monocot crops, we transiently expressed PMR4 under control of the 35S promoter in leaves of barley (Hordeum vulgare) seedlings, which were subsequently inoculated with the virulent powdery mildew Blumeria graminis f. sp. hordei
PMR4 did not seem to be required for penetration resistance to powdery mildew in the A. thaliana mlo2 (MILDEW RESISTANCE LOCUS O 2) mutant [10], whereas an inhibition of callose synthesis in a barley (Hordeum vulgare) mlo mutant resulted in an increased powdery mildew penetration [11]
Summary
The plant cell wall is one of the first lines of defense against invading pathogens. A strengthening of the cell. Wall by callose deposition in so called papillae is considered as an important part of the basal plant resistance mechanism against penetration [1]. Callose is a linear polysaccharide, which consists of (1,3)-β-linked glucose monomers with some (1,6)-β-branches [2]. It is synthesized by membrane-bound callose synthases [3], which might be organized in multiprotein complexes [4] and use UDP-glucose as substrate [5]. Among the 12 callose synthases in A. thaliana, PMR4 (POWDERY MILDEW RESITANT 4, called GLUCAN SYNTHASE LIKE 5) is responsible for woundand pathogen-induced callose formation [8,9]. The overexpression of PMR4 in A. thaliana led to an early enhanced callose deposition after powdery mildew infection, which conferred complete penetration resistance [3,13]. Based on the scientific and economic importance of powdery mildews and especially Blumeria graminis [14], we wanted to evaluate whether modification of callose biosynthesis would increase penetration resistance to an adapted powdery mildew in barley
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
