Two sides of a leaf blade: Blumeria graminis needs chemical cues in cuticular waxes of Lolium perenne for germination and differentiation

Abstract

Plant surface characteristics were repeatedly shown to play a pivotal role in plant-pathogen interactions. The abaxial leaf surface of perennial ryegrass (Lolium perenne) is extremely glossy and wettable compared to the glaucous and more hydrophobic adaxial surface. Earlier investigations have demonstrated that the abaxial leaf surface was rarely infected by powdery mildew (Blumeria graminis), even when the adaxial surface was densely colonized. This led to the assumption that components of the abaxial epicuticular leaf wax might contribute to the observed impairment of growth and development of B. graminis conidia on abaxial surfaces of L. perenne. To re-assess this hypothesis, we analyzed abundance and chemical composition of L. perenne ab- and adaxial epicuticular wax fractions. While the adaxial epicuticular waxes were dominated by primary alcohols and esters, the abaxial fraction was mainly composed of n-alkanes and aldehydes. However, the major germination and differentiation inducing compound, the C26-aldehyde n-hexacosanal, was not present in the abaxial epicuticular waxes. Spiking of isolated abaxial epicuticular Lolium waxes with synthetically produced n-hexacosanal allowed reconstituting germination and differentiation rates of B. graminis in an in vitro germination assay using wax-coated glass slides. Hence, the absence of the C26-aldehyde from the abaxial surface in combination with a distinctly reduced surface hydrophobicity appears to be primarily responsible for the failure of normal germling development of B. graminis on the abaxial leaf surfaces of L. perenne.

Tissue- and Cell-Type Specific Transcriptome Profiling of Expanding Tomato Fruit Provides Insights into Metabolic and Regulatory Specialization and Cuticle Formation

“…In the fruit pericarp, the leaves have two surfaces, with the inner and outer epidermis corresponding to the adaxial and abaxial leaf surfaces, respectively. Distinct differences in the adaxial and abaxial cuticle composition of leaves have previously been noted (Holloway, 1973;Ringelmann et al, 2009), and in this study, we confirmed that the inner epidermal cells form a thin cuticle with a cutin composition that differs from that of the far thicker outer epidermal cuticle. In this regard, the ontogeny of the fruit pericarp as a modified leaf is revealed.…”

The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Arabidopsis thaliana Crown Galls

“…N-Tetracosane (C 24 ; SigmaAldrich) was added as an internal standard to all samples, and the solvent was evaporated under a gentle stream of N 2 . Chemical analyses were performed as described by Ringelmann et al (2009) using a 7890A gas chromatograph (Agilent Technologies) and the column type 30 m DB-1HT (0.32 mm i.d., degrees of freedom = 0.1 mm; Agilent Technologies) for quantification. Accordingly, single compounds (where applicable as trimethylsilyl derivatives) were identified by comparison of their mass spectra with those of published data, commercially available databases, as well as authentic standards.…”

The Formation and Function of Plant Cuticles

“…In addition to the lotus effect that promotes the washing of spores from the plant surface before germination, there are several indications that the epicuticular wax structures and composition are important in determining fungal pathogen development and, thus, pathogenicity. The C26 aldehyde n-hexacosanyl, a component of cuticular wax in many species of the Poaceae, can induce in vitro appressorium formation by the powdery mildew Blumeria graminis (Tsuba et al, 2002;Ringelmann et al, 2009;Hansjakob et al, 2010). This observation is further corroborated by studies of the maize mutant glossy1, which does not accumulate aldehydes in its wax complement.…”