Genes ScBx1 and ScIgl—Competitors or Cooperators?

Anna Wlazło,Mariusz Kowalczyk,Leszek Bolibok,Tomasz Krępski,Monika Rakoczy-Trojanowska,Marek D Koter,Magdalena Święcicka,Anna Stochmal

doi:10.3390/genes11020223

Abstract

Two genes, Bx1 and Igl, both encoding indole-3-glycerol phosphate lyase (IGL), are believed to control the conversion of indole-3-glycerol phosphate (IGP) to indole. The first of these has generally been supposed to be regulated developmentally, being expressed at early stages of plant development with the indole being used in the benzoxazinoid (BX) biosynthesis pathway. In contrast, it has been proposed that the second one is regulated by stresses and that the associated free indole is secreted as a volatile. However, our previous results contradicted this. In the present study, we show that the ScIgl gene takes over the role of ScBx1 at later developmental stages, between the 42nd and 70th days after germination. In the majority of plants with silenced ScBx1 expression, ScIgl was either expressed at a significantly higher level than ScBx1 or it was the only gene with detectable expression. Therefore, we postulate that the synthesis of indole used in BX biosynthesis in rye is controlled by both ScBx1 and ScIgl, which are both regulated developmentally and by stresses. In silico and in vivo analyses of the promoter sequences further confirmed our hypothesis that the roles and modes of regulation of the ScBx1 and ScIgl genes are similar.

Highlights

Benzoxazinoids (BXs) are secondary metabolites synthesized by many species from the Poaceae family and, sporadically, by several dicots
The first step, a branch point in BX biosynthesis, that occurs in chloroplasts is the conversion of indole-3-glycerol phosphate (IGP) to indole
The reactions take place in other cell compartments: four subsequent reactions leading to the synthesis of 2,4-dihydroxy-1,4-benzoxazin-3(4H)-one (DIBOA) followed by the glycosylation of DIBOA to 2-O-β-glucoside (GDIBOA) and O-methylation leading to 2,4,7-trihydroxy-1,4-benzoxazin-3-one glucoside (GTRIBOA), 2,4-dihydroxy-7-methoxy1,4-benzoxazin-3(4H)-one (DIMBOA) glucoside (GDIMBOA), and 4,7-dimethoxy-2-{[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}-3,4-dihydro-2H-1,4-benzoxazn-3-one glucoside (GHDMBOA)

Summary

Introduction

Benzoxazinoids (BXs) are secondary metabolites synthesized by many species from the Poaceae family and, sporadically, by several dicots. The reactions take place in other cell compartments: four subsequent reactions leading to the synthesis of 2,4-dihydroxy-1,4-benzoxazin-3(4H)-one (DIBOA) (in endoplasmic reticulum) followed by the glycosylation of DIBOA to 2-O-β-glucoside (GDIBOA) (stored in vacuoles) and O-methylation leading to 2,4,7-trihydroxy-1,4-benzoxazin-3-one glucoside (GTRIBOA), 2,4-dihydroxy-7-methoxy1,4-benzoxazin-3(4H)-one (DIMBOA) glucoside (GDIMBOA), and 4,7-dimethoxy-2-{[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}-3,4-dihydro-2H-1,4-benzoxazn-3-one glucoside (GHDMBOA). These glucosides are stored in the vacuoles. Ten orthologs of maize Bx genes, namely, ScBx1–ScBx7, ScIgl, Scglu, and ScGT (the last one corresponding to maize Bx8 and Bx9), have been isolated in the last decade [7,8,9,10,11]. In addition to Bx1, two other genes, namely, Igl and TSA, control the transformation

Objectives

Methods

Results

Conclusion