title: Benzoxazinoid metabolites regulate innate immunity against aphids and fungi in maize.
abstract: Benzoxazinoids (BXs), such as 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), are secondary metabolites in grasses. The first step in BX biosynthesis converts indole-3-glycerol phosphate into indole. In maize (Zea mays), this reaction is catalyzed by either BENZOXAZINELESS1 (BX1) or INDOLE GLYCEROL PHOSPHATE LYASE (IGL). The Bx1 gene is under developmental control and is mainly responsible for BX production, whereas the Igl gene is inducible by stress signals, such as wounding, herbivory, or jasmonates. To determine the role of BXs in defense against aphids and fungi, we compared basal resistance between Bx1 wild-type and bx1 mutant lines in the igl mutant background, thereby preventing BX production from IGL. Compared to Bx1 wild-type plants, BX-deficient bx1 mutant plants allowed better development of the cereal aphid Rhopalosiphum padi, and were affected in penetration resistance against the fungus Setosphaeria turtica. At stages preceding major tissue disruption, R. padi and S. turtica elicited increased accumulation of DIMBOA-glucoside, DIMBOA, and 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one-glucoside (HDMBOA-glc), which was most pronounced in apoplastic leaf extracts. Treatment with the defense elicitor chitosan similarly enhanced apoplastic accumulation of DIMBOA and HDMBOA-glc, but repressed transcription of genes controlling BX biosynthesis downstream of BX1. This repression was also obtained after treatment with the BX precursor indole and DIMBOA, but not with HDMBOA-glc. Furthermore, BX-deficient bx1 mutant lines deposited less chitosan-induced callose than Bx1 wild-type lines, whereas apoplast infiltration with DIMBOA, but not HDMBOA-glc, mimicked chitosan-induced callose. Hence, DIMBOA functions as a defense regulatory signal in maize innate immunity, which acts in addition to its well-characterized activity as a biocidal defense metabolite.
authors: Rothamsted Research, Centre for Sustainable Pest and Disease Management, Harpenden AL5 4JQ, United Kingdom.
authors: Shakoor
authors: S
authors: Ahmad
authors: Nathalie
authors: N
authors: Veyrat
authors: Ruth
authors: R
authors: Gordon-Weeks
authors: Yuhua
authors: Y
authors: Zhang
authors: Janet
authors: J
authors: Martin
authors: Lesley
authors: L
authors: Smart
authors: Gaétan
authors: G
authors: Glauser
authors: Matthias
authors: M
authors: Erb
authors: Victor
authors: V
authors: Flors
authors: Monika
authors: M
authors: Frey
authors: Jurriaan
authors: J
authors: Ton
mesh_terms: D000818:Animals; D001042:Aphids / Q000502:physiology*; D048588:Benzoxazines / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D005658:Fungi / Q000502:physiology*; D017343:Genes, Plant; D007113:Immunity, Innate; D018749:RNA, Plant / Q000302:isolation & purification; D060888:Real-Time Polymerase Chain Reaction; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics / Q000276:immunology* / Q000469:parasitology
chemical_list: D048588:Benzoxazines; D018076:DNA, Complementary; D018749:RNA, Plant