Chemical Signals from Avocado Surface Wax Trigger Germination and Appressorium Formation in Colletotrichum gloeosporioides

Abstract

l h e surface wax of the host, avocado (Persea americana) fruit, induced germination and appressorium formation in the spores of Colletotrichum gloeosporioides. Waxes from nonhost plants did not induce appressorium formation in this fungus, and avocado wax did not induce appressorium formation in most Colletotrichum species that infect other hosts. Bioassays of the thin-layer chromatographic fractions of the avocado wax showed that the fatty alcohol fraction was the main appressorium-inducing component. Testing of authentic n-C, to n-Cs2 fatty alcohols revealed that C,, and longer-chain alcohols induced appressorium formation. Casliquid chromatographylmass spectrometry analysis of free fatty alcohols revealed that avocado wax contains a high content of very long chains. Waxes from nonhost plants containing an even higher content of the very long-chain alcohols did not induce appressorium formation. Waxes from nonhost plants strongly inhibited appressorium induction by avocado wax. Thus, a favorable balance between appressorium-inducing very iong-chain fatty alcohols and the absence of inhibitors allows the fungus to use the host surface wax to trigger germination and differentiation of infection structures in the pathogen.

Overexpression of ArabidopsisECERIFERUM1Promotes Wax Very-Long-Chain Alkane Biosynthesis and Influences Plant Response to Biotic and Abiotic Stresses

“…The cuticle permeability modification in these transgenic plants could be responsible for a less efficient perception of the fungal elicitors, delaying the activation of the defense responses. Furthermore, it has been shown that leaf or fruit waxes could contain active components that induce germination and appressorium formation by fungal pathogens (Podila et al, 1993;Hegde and Kolattukudy, 1997;Reisige et al, 2006). Therefore, VLC alkanes accumulated on the CER1ox leaf surface could act as components activating the development of the fungus or could deeply perturb the hydrophobic properties of the leaf cuticle and allow better fungus propagation.…”

Apoplastic Diffusion Barriers in Arabidopsis

“…They act as substrates for the attachment of colonizing organisms to the leaf surface (Clement et al, 1994;Tucker and Talbot, 2001), and they also play crucial roles in plant-pathogen and plant-pest signaling (Kolattukudy et al, 1995;Chassot and Métraux, 2005;Reina-Pinto and Yephremov, 2009). It is well established that some wax components, such as triterpenoids and aldehydes, are important in pre-invasion processes, including spore germination and appressorium formation, in different plant species (Podila et al, 1993;Gniwotta et al, 2005;Reisige et al, 2006;Inada and Savory, 2011). Inada and Savory (Inada and Savory, 2011) recently demonstrated in Arabidopsis that pre-penetration processes in the biotrophic fungus Golovinomyces orontii were suppressed on cauline leaves, stems, siliques and roots compared to rosette leaves.…”

Influence of epiphytic micro‐organisms on leaf wettability: wetting of the upper leaf surface of Juglans regia and of model surfaces in relation to colonization by micro‐organisms

“…Little is known about cuticular functions with regard to saprophytic microbial life on leaf surfaces. Interactions between the cuticle and micro-organisms are pertinent during cellular adhesion (Young & Kauss, 1984 ;Kuo & Hoch, 1996), growth and reproduction, differentiation processes (Uchiyama & Okuyama, 1990 ;Podila, Rogers & Kolattukudy, 1993 ;D. Knoll and L. Schreiber Flaishman, Hwang & Kolattukudy, 1995) and metabolic activities of micro-organisms that eventually influence cutin and wax composition.…”