Carbohydrate elicitor-induced plant immunity: Advances and prospects

Chitin/cellulose nanofiber complex from spent mushroom substrate systemically induces plant disease resistance through its cellulose-derived function

Spent mushroom substrate (SMS) is a major agricultural waste generated as a by-product of industrial mushroom cultivation. To valorize SMS, we developed a method to convert it to a form of nanofiber dispersion, chitin/cellulose nanofiber complex (CCNFC), via nanofibrillation. CCNFC application induces plant disease resistance, local immune response, and systemic disease resistance. Because chitin nanofibers (NF) also induce these defense responses, their function has been proposed to contribute to CCNFC-induced disease resistance. Here, we aimed to determine the precise mode of action of CCNFC in inducing plant disease resistance. The local immune response and systemic disease resistance induced by CCNFC were not compromised in Arabidopsis and rice mutants for lysin motif-type pattern recognition receptors involved in chitin perception. Transcriptome analysis revealed similar systemic transcriptional responses in CCNFC- and cellulose NF-treated Arabidopsis plants. Cellulose NF-induced systemic disease resistance but not local immune response. Thus, the local immune response triggered by CCNFC also requires another component(s) in CCNFC other than cellulose, accompanied by chitin. In contrast, the systemic disease resistance induced by CCNFC could be caused mainly by cellulose NF.

Biochemical Defence of Plants against Parasitic Nematodes

Plant parasitic nematodes (PPNs), such as Meloidogyne spp., Heterodera spp. and Pratylenchus spp., are obligate parasites on a wide range of crops, causing significant agricultural production losses worldwide. These PPNs mainly feed on and within roots, impairing both the below-ground and the above-ground parts, resulting in reduced plant performance. Plants have developed a multi-component defence mechanism against diverse pathogens, including PPNs. Several natural molecules, ranging from cell wall components to secondary metabolites, have been found to protect plants from PPN attack by conferring nematode-specific resistance. Recent advances in omics analytical tools have encouraged researchers to shed light on nematode detection and the biochemical defence mechanisms of plants during nematode infection. Here, we discuss the recent progress on revealing the nematode-associated molecular patterns (NAMPs) and their receptors in plants. The biochemical defence responses of plants, comprising cell wall reinforcement; reactive oxygen species burst; receptor-like cytoplasmic kinases; mitogen-activated protein kinases; antioxidant activities; phytohormone biosynthesis and signalling; transcription factor activation; and the production of anti-PPN phytochemicals are also described. Finally, we also examine the role of epigenetics in regulating the transcriptional response to nematode attack. Understanding the plant defence mechanism against PPN attack is of paramount importance in developing new, effective and sustainable control strategies.