An oat species lacking avenacin is susceptible to infection by Gaeumannomyces graminis var. tritici

Osbourn, Anne; Clarke, Belinda; Lunness, Patricia; Scott, P. R.; Daniels, Michael J.

doi:10.1016/s0885-5765(05)80042-6

Cited by 119 publications

(77 citation statements)

References 14 publications

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“…Previously, we showed that avenacin A-1 is the major UV fluorescent compound in wild-type oat roots (Osbourn et al, 1994). Confocal microscopy using excitation and emission conditions that detect avenacin A-1 revealed that the fluorescence associated with this saponin appears to be localized in the vacuoles of the root epidermal cells ( Figure 5A).…”

Section: Saponin Localizationmentioning

confidence: 79%

“…Production of secondary metabolites is usually tightly regulated in plants, since the pathway end products and also their biosynthetic intermediates may have phytotoxic activity. Avenacin A-1 accumulates in the epidermal cells of oat roots, and its synthesis is highly localized (Turner, 1960;Osbourn et al, 1994). Expression of Sad1 and Sad2 occurs primarily in these cells and is under strict developmental control (Haralampidis et al, 2001a;Qi et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Sad3andSad4Are Required for Saponin Biosynthesis and Root Development in Oat

et al. 2008

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Avenacins are antimicrobial triterpene glycosides that are produced by oat (Avena) roots. These compounds confer broadspectrum resistance to soil pathogens. Avenacin A-1, the major avenacin produced by oats, is strongly UV fluorescent and accumulates in root epidermal cells. We previously defined nine loci required for avenacin synthesis, eight of which are clustered. Mutants affected at seven of these (including Saponin-deficient1 [Sad1], the gene for the first committed enzyme in the pathway) have normal root morphology but reduced root fluorescence. In this study, we focus on mutations at the other two loci, Sad3 (also within the gene cluster) and Sad4 (unlinked), which result in stunted root growth, membrane trafficking defects in the root epidermis, and root hair deficiency. While sad3 and sad4 mutants both accumulate the same intermediate, monodeglucosyl avenacin A-1, the effect on avenacin A-1 glucosylation in sad4 mutants is only partial. sad1/sad1 sad3/sad3 and sad1/sad1 sad4/sad4 double mutants have normal root morphology, implying that the accumulation of incompletely glucosylated avenacin A-1 disrupts membrane trafficking and causes degeneration of the epidermis, with consequential effects on root hair formation. Various lines of evidence indicate that these effects are dosage-dependent. The significance of these data for the evolution and maintenance of the avenacin gene cluster is discussed.

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Section: Saponin Localizationmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Sad3andSad4Are Required for Saponin Biosynthesis and Root Development in Oat

et al. 2008

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“…Furthermore, mRNA in situ hybridization revealed that expression of SCPL1 within the root tip is restricted to the epidermal cells ( Figure 2C), as is the case for Sad1 and Sad2 (Haralampidis et al, 2001;Qi et al, 2006). These cells are the site of avenacin accumulation (Osbourn et al, 1994;Haralampidis et al, 2001). The expression pattern of SCPL1 is therefore consistent with a role for SCPL1 in avenacin biosynthesis.…”

Section: Scpl1 Is Synonymous With Sad7mentioning

confidence: 81%

A Serine Carboxypeptidase-Like Acyltransferase Is Required for Synthesis of Antimicrobial Compounds and Disease Resistance in Oats

et al. 2009

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Serine carboxypeptidase-like (SCPL) proteins have recently emerged as a new group of plant acyltransferases. These enzymes share homology with peptidases but lack protease activity and instead are able to acylate natural products. Several SCPL acyltransferases have been characterized to date from dicots, including an enzyme required for the synthesis of glucose polyesters that may contribute to insect resistance in wild tomato (Solanum pennellii) and enzymes required for the synthesis of sinapate esters associated with UV protection in Arabidopsis thaliana. In our earlier genetic analysis, we identified the Saponin-deficient 7 (Sad7) locus as being required for the synthesis of antimicrobial triterpene glycosides (avenacins) and for broad-spectrum disease resistance in diploid oat (Avena strigosa). Here, we report on the cloning of Sad7 and show that this gene encodes a functional SCPL acyltransferase, SCPL1, that is able to catalyze the synthesis of both N-methyl anthraniloyl-and benzoyl-derivatized forms of avenacin. Sad7 forms part of an operon-like gene cluster for avenacin synthesis. Oat SCPL1 (SAD7) is the founder member of a subfamily of monocot-specific SCPL proteins that includes predicted proteins from rice (Oryza sativa) and other grasses with potential roles in secondary metabolism and plant defense.

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“…Other antimicrobial secondary metabolites exhibit an abundant accumulation in peripheral root tissues. Saponins have been localized to the epidermal cells of oat (Avena sativa) roots as an initial barrier to fungal infection (Osbourn et al, 1994;Osbourn, 1996). Flavonoids and flavonoid biosynthetic enzymes also accumulate in the epidermis and adjacent cortical cells of Arabidopsis thaliana roots (Saslowsky and Winkel-Shirley, 2001).…”

Section: Discussionmentioning

confidence: 99%

Cell Type–Specific Localization of Transcripts Encoding Nine Consecutive Enzymes Involved in Protoberberine Alkaloid Biosynthesis

2005

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Molecular clones encoding nine consecutive biosynthetic enzymes that catalyze the conversion of L-dopa to the protoberberine alkaloid (S)-canadine were isolated from meadow rue (Thalictrum flavum ssp glaucum). The predicted proteins showed extensive sequence identity with corresponding enzymes involved in the biosynthesis of related benzylisoquinoline alkaloids in other species, such as opium poppy (Papaver somniferum). RNA gel blot hybridization analysis showed that gene transcripts for each enzyme were most abundant in rhizomes but were also detected at lower levels in roots and other organs. In situ RNA hybridization analysis revealed the cell type-specific expression of protoberberine alkaloid biosynthetic genes in roots and rhizomes. In roots, gene transcripts for all nine enzymes were localized to immature endodermis, pericycle, and, in some cases, adjacent cortical cells. In rhizomes, gene transcripts encoding all nine enzymes were restricted to the protoderm of leaf primordia. The localization of biosynthetic gene transcripts was in contrast with the tissue-specific accumulation of protoberberine alkaloids. In roots, protoberberine alkaloids were restricted to mature endodermal cells upon the initiation of secondary growth and were distributed throughout the pith and cortex in rhizomes. Thus, the cell type-specific localization of protoberberine alkaloid biosynthesis and accumulation are temporally and spatially separated in T. flavum roots and rhizomes, respectively. Despite the close phylogeny between corresponding biosynthetic enzymes, distinct and different cell types are involved in the biosynthesis and accumulation of benzylisoquinoline alkaloids in T. flavum and P. somniferum. Our results suggest that the evolution of alkaloid metabolism involves not only the recruitment of new biosynthetic enzymes, but also the migration of established pathways between cell types.

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An oat species lacking avenacin is susceptible to infection by Gaeumannomyces graminis var. tritici

Cited by 119 publications

References 14 publications

Sad3andSad4Are Required for Saponin Biosynthesis and Root Development in Oat

Sad3andSad4Are Required for Saponin Biosynthesis and Root Development in Oat

A Serine Carboxypeptidase-Like Acyltransferase Is Required for Synthesis of Antimicrobial Compounds and Disease Resistance in Oats

Cell Type–Specific Localization of Transcripts Encoding Nine Consecutive Enzymes Involved in Protoberberine Alkaloid Biosynthesis

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