| Summary: | Two genes, <i>Bx1</i> and <i>Igl</i>, 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 <i>ScIgl</i> gene takes over the role of <i>ScBx1</i> at later developmental stages, between the 42nd and 70th days after germination. In the majority of plants with silenced <i>ScBx1</i> expression, <i>ScIgl</i> was either expressed at a significantly higher level than <i>ScBx1</i> 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 <i>ScBx1</i> and <i>ScIgl</i>, 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 <i>ScBx1</i> and <i>ScIgl</i> genes are similar.
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