β-glucan: Crucial component of the fungal cell wall and elusive MAMP in plants

Plant innate immunity relies in first place on the detection of invading microbes. Thus, plants evolved receptors to sense unique molecules of the microbe, the so called microbe-associated molecular patterns or MAMPs. The best studied fungal MAMP is chitin, an important structural building block of the fungal cell wall. Over the past years several plant receptors for chitin have been characterized as well as different strategies adopted by fungi to evade chitin recognition. Despite its strong activity as an elicitor of plant defense chitin represents only a small percentage of the cell wall of most fungi compared to other complex sugars. beta-glucan, the most abundant fungal cell wall polysaccharide, also serves as a MAMP, but the mechanisms of beta-glucan perception and signaling in plants are largely unknown. In contrast to that the beta-glucan recognition and signaling machineries are well characterized in mammals. The C-type lectin receptor Dectin-1 is a key component of these machineries. In this review we describe valuable knowledge about the existence of at least one beta-glucan receptor in plants and about the hindrances in beta-glucan research. Additionally we discuss possible future perspectives of glucan research and the possibility to transfer the gathered knowledge from mammalian systems to plants. (C) 2015 The Authors. Published by Elsevier Inc.