A shared <i>cis</i>-regulatory module activates transcription in the suspensor of plant embryos.

Abstract

The mechanisms controlling the transcription of gene sets in specific regions of a plant embryo shortly after fertilization remain unknown. Previously, we showed that G564 mRNA, encoding a protein of unknown function, accumulates to high levels in the giant suspensor of both Scarlet Runner Bean (SRB) and Common Bean embryos, and a <i>cis</i>-regulatory module containing three unique DNA sequences, designated as the 10-bp, Region 2, and Fifth motifs, is required for <i>G564</i> suspensor-specific transcription [Henry KF, et al. (2015) <i>Plant Mol Biol</i> 88:207-217; Kawashima T, et al. (2009) <i>Proc Natl Acad Sci USA</i> 106:3627-3632]. We tested the hypothesis that these motifs are also required for transcription of the SRB <i>GA 20-oxidase</i> gene, which encodes a gibberellic acid hormone biosynthesis enzyme and is coexpressed with <i>G564</i> at a high level in giant bean suspensors. We used deletion and gain-of-function experiments in transgenic tobacco embryos to show that two <i>GA 20-oxidase</i> DNA regions are required for suspensor-specific transcription, one in the 5' UTR (+119 to +205) and another in the 5' upstream region (-341 to -316). Mutagenesis of sequences in these two regions determined that the <i>cis</i>-regulatory motifs required for <i>G564</i> suspensor transcription are also required for <i>GA 20-oxidase</i> transcription within the suspensor, although the motif arrangement differs. Our results demonstrate the flexibility of motif positioning within a <i>cis</i>-regulatory module that activates gene transcription within giant bean suspensors and suggest that <i>G564</i> and <i>GA 20-oxidase</i> comprise part of a suspensor gene regulatory network.