The Roots of Rye (Secale cereale L.) Are Capable of Synthesizing Benzoxazinoids.

Monika Rakoczy-Trojanowska,Elżbieta Różańska,Mariusz Kowalczyk,Magdalena Święcicka,Beata Bakera,Wojciech Burza,Bartosz M Szabała

doi:10.3390/ijms22094656

Abstract

According to current opinion, the first step of benzoxazinoids (BXs) synthesis, that is, the conversion of indole-3-glycerol phosphate to indole, occurs exclusively in the photosynthesising parts of plants. However, the results of our previous work and some other studies suggest that this process may also occur in the roots. In this study, we provide evidence that the first step of BXs synthesis does indeed occur in the roots of rye seedlings. We detected ScBx1 transcripts, BX1 enzyme, and six BXs (2-hydroxy-1,4-benzoxazin-3-one, 2,4-dihydroxy-1,4-benzoxazin-3-one, (2R)-2-O-β-d-glucopyranosyl-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one glucoside, 2,4-dihydroxy- 7-methoxy-1,4-benzoxazin-3-one, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside, and 6-methoxy-2-benzoxazolinone) in the roots developed from seeds deprived of the coleoptile at 2 days after sowing (i.e., roots without contact with aerial parts). In roots regenerated in vitro, both ScBx1 transcripts and BX1 enzyme were detected at a low but still measurable levels. Thus, BXs are able to be synthesised in both the roots and above-ground parts of rye plants.

Highlights

Benzoxazinoids (BXs), secondary metabolites synthesised by several species of the Poaceae family, play an important role in biotic and abiotic stress resistance, and in allelopathy
Many studies on different aspects BX biosynthesis over the past 50 years have reported that this class of metabolites is present in roots, root exudates, or root extracts of such species as maize [6,21,22,23], common wheat [24,25,26,27], emmer wheat [28], and rye [2,14,15,16,24,29]
We proved that one more gene, ScIgl, controls the first step of BX biosynthesis at later developmental stages [11] and that this gene is expressed in roots of rye [14]

Summary

Introduction

Benzoxazinoids (BXs), secondary metabolites synthesised by several species of the Poaceae family, play an important role in biotic and abiotic stress resistance, and in allelopathy. Common rye (Secale cereale L.) is among the species producing BXs at a high level [1,2,3]. BX produced and secreted by rye roots makes it a suitable crop for sustainable weed control and organic farming [3]. The glycosylation of DIBOA and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) results in the production of (2R)-2-O-β-D-glucopyranosyl-4-hydroxy-(2H)-1,4benzoxazin-3(4H)-one glucoside (GDIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin3-one glucoside (GDIMBOA), respectively. The O-methylation of DIBOA and DIMBOA yields 2,4,7-trihydroxy-1,4-benzoxazin-3-one glucoside (GTRIBOA) and 2-hydroxy-4,7dimethoxy-1,4-benzoxazin-3-one glucoside (GHDMBOA), respectively. Hydroxylation reactions convert GDIBOA to DIBOA and GDIMBOA to DIMBOA [3,4,5,6,7]

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