Changes in benzoxazinoid contents and the expression of the associated genes in rye (Secale cereale L.) due to brown rust and the inoculation procedure.

Magdalena Święcicka,Agnieszka Grądzielewska,Mariusz Kowalczyk,Marta Dmochowska-Boguta,Wacław Orczyk,Monika Rakoczy-Trojanowska,Anna Stochmal,Leszek Bolibok

doi:10.1371/journal.pone.0233807

Abstract

Benzoxazinoids (BXs) are secondary metabolites with diverse functions, but are primarily involved in protecting plants, mainly from the family Poaceae, against insects and fungal pathogens. Rye is a cereal crop that is highly resistant to biotic stresses. However, its susceptibility to brown rust caused by Puccinia recondita f. sp. secalis (Prs) is still a major problem affecting its commercial production. Additionally, the genetic and metabolic factors related to this disease remain poorly characterized. In this study, we investigated whether and to what extent the brown rust infection and the inoculation procedure affect the contents of specific BXs (HBOA, GDIBOA, DIBOA, GDIMBOA, DIMBOA, and MBOA) and the expression of genes related to BX (ScBx1–5, ScIgl, and Scglu). We revealed that treatments with water and a urediniospore suspension usually downregulate gene expression levels. Moreover, HBOA and DIBOA contents decreased, whereas the contents of the remaining metabolites increased. Specifically, the MBOA content increased more after the mock treatment than after the Prs treatment, whereas the increase in GDIBOA and GDIMBOA levels was usually due to the Prs infection, especially at two of the most critical time-points, 17 and 24 h post-treatment. Therefore, GDIBOA and GDIMBOA are glucosides that are important components of rye defence responses to brown rust. Furthermore, along with MBOA, they protect rye against the stress associated with the inoculation procedure used in this study.

Highlights

Benzoxazinoids (BXs) are secondary metabolites synthesized mainly by species belonging to the family Poaceae, including rye (Secale cereale L.)
Other reactions include the glycosylation of DIBOA to produce 2-O-β-glucoside (GDIBOA) and O-methylation to generate 2,4,7-trihydroxy-1,4-benzoxazin-3-one glucoside (GTRIBOA) as well as the glycosylation of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) to produce 2,4-dihydroxy7-methoxy-1,4-benzoxazin-3-one glucoside (GDIMBOA) and O-methylation to generate 4,7-dimethoxy-2-{[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}-3,4-dihydro-2H1,4-benzoxazin-3-one glucoside (GHDMBOA)
The objective of this study was to determine whether a Puccinia recondita f. sp. secalis (Prs) infection and the subsequent disease development as well as the inoculation procedure itself influence the expression levels and profiles of the following seven genes: ScBx1–ScBx5, ScIgl, and Scglu, of which, the first six control the production of six BXs [2-hydroxy-4H-1,4-benzoxazin-3-one (HBOA), GDIBOA, DIBOA, GDIMBOA, DIMBOA, and 6-methoxybenzoxazolinone (MBOA)] and the last one mediates the hydroxylation of glucosides to aglucones

Summary

Introduction

Benzoxazinoids (BXs) are secondary metabolites synthesized mainly by species belonging to the family Poaceae, including rye (Secale cereale L.). Several studies have confirmed that BX biosynthesis comprises several steps [1,2,3,4,5,6]. Indole-3-glycerol phosphate is converted to indole, which is transformed to indolin-1-one. Three monooxidations result in the synthesis of 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA). Other reactions include the glycosylation of DIBOA to produce 2-O-β-glucoside (GDIBOA) and O-methylation to generate 2,4,7-trihydroxy-1,4-benzoxazin-3-one glucoside (GTRIBOA) as well as the glycosylation of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) to produce 2,4-dihydroxy7-methoxy-1,4-benzoxazin-3-one glucoside (GDIMBOA) and O-methylation to generate 4,7-dimethoxy-2-{[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}-3,4-dihydro-2H1,4-benzoxazin-3-one glucoside (GHDMBOA). Hydroxylations convert GDIBOA and GDIMBOA to DIBOA and DIMBOA, respectively

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