Hydroxamic Acids Derived from 2-Hydroxy-2H-1,4-Benzoxazin-3(4H)-one: Key Defense Chemicals of Cereals

Abstract

Many cereals accumulate hydroxamic acids derived from 2-hydroxy-2H-1,4-benzoxazin-3(4H)-one. These benzoxazinoid hydroxamic acids are involved in defense of maize against various lepidopteran pests, most notably the European corn borer, in defense of cereals against various aphid species, and in allelopathy affecting the growth of weeds associated with rye and wheat crops. The role of benzoxazinoid hydroxamic acids in defense against fungal infection is less clear and seems to depend on the nature of the interactions at the plant-fungus interface. Efficient use of benzoxazinoid hydroxamic acids as resistance factors has been limited by the inability to selectively increase their levels at the plant growth stage and the plant tissues where they are mostly needed for a given pest. Although the biosynthesis of benzoxazinoid hydroxamic acids has been elucidated, the genes and mechanisms controlling their differential expression in different plant tissues and along plant ontogeny remain to be unraveled.

Dynamic maize responses to aphid feeding are revealed by a time series of transcriptomic and metabolomic assays

“…5A and 6A), a class of specialized metabolites in grasses that provide defense against insect herbivory (Frey et al, 2009;Ahmad et al, 2011). Ten enzymes (Bx1-Bx9 and Igl1) catalyze the formation of DIMBOA-Glc from indole-3-glycerol phosphate (Frey et al, 2009;Niemeyer, 2009; This is followed by methylation into HDMBOA-Glc through the activity of three Bx10 enzymes Mijares et al, 2013). Transcripts of Bx1 (GRMZM2G085381), Bx2 (GRMZM2G085661), Bx6 (GRMZM6G617209), and Bx7 (GRMZM2G441753) were significantly induced at early time points as well as at 96 h after aphid attack.…”

“…The predominant benzoxazinoids in maize foliar tissue are 4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc) and 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc; Frey et al, 1997Frey et al, , 2009). These compounds inhibit the growth of fungi, arrest insect herbivore growth, and cause allelopathic effects (Niemeyer, 2009;Ahmad et al, 2011). Benzoxazinoids are stored in a glucoside form that has reduced toxicity compared with the aglycones, which are produced upon cell disruption during pathogen or herbivore attack (Frey et al, 2009).…”

Benzoxazinoid Metabolites Regulate Innate Immunity against Aphids and Fungi in Maize

“…It is commonly assumed that BX-glucosides are hydrolyzed by plastid-targeted b-glucosidases upon tissue disruption, which results in the release of biocidal aglycone BXs (Morant et al, 2008). Since their discovery as plant secondary metabolites, many investigations have focused on their role in plant defense against herbivorous insects and pathogens (Niemeyer, 1988(Niemeyer, , 2009. Most of these studies revealed positive correlations between resistance and BX levels in cereal varieties or inbred populations, or biocidal activity when added to artificial growth medium (for review, see Niemeyer, 2009).…”

Mapping resistance to the bird cherry-oat aphid and the greenbug in wheat using sequence-based genotyping

“…There are 14 previously reported S. graminum resistance genes in wheat and wheat relatives, and nine of those have been found in the chromosome 7DL from A. tauschii (McIntosh et al 2010). However, six of the nine genes reported in 7DL may be allelic or closely linked to Gb3 (Zhu et al 2005).…”

“…Currently there are 14 major genes for resistance to S. graminum in wheat that have been identified (McIntosh et al 2010;Crespo-Herrera 2012). Of those, one is from Triticum turgidum L., two from Secale cereale L., one from T. aestivum, one from Aegilops speltoides Tausch, and 9 from A. tauschii.…”