A cis-regulatory module activating transcription in the suspensor contains five cis-regulatory elements.

Kelli F Henry,Robert B Goldberg,Tomokazu Kawashima

doi:10.1007/s11103-015-0308-z

Abstract

Little is known about the molecular mechanisms by which the embryo proper and suspensor of plant embryos activate specific gene sets shortly after fertilization. We analyzed the upstream region of the Scarlet Runner Bean (Phaseolus coccineus) G564 gene in order to understand how genes are activated specifically in the suspensor during early embryo development. Previously, we showed that a 54-bp fragment of the G564 upstream region is sufficient for suspensor transcription and contains at least three required cis-regulatory sequences, including the 10-bp motif (5′-GAAAAGCGAA-3′), the 10 bp-like motif (5′-GAAAAACGAA-3′), and Region 2 motif (partial sequence 5′-TTGGT-3′). Here, we use site-directed mutagenesis experiments in transgenic tobacco globular-stage embryos to identify two additional cis-regulatory elements within the 54-bp cis-regulatory module that are required for G564 suspensor transcription: the Fifth motif (5′-GAGTTA-3′) and a third 10-bp-related sequence (5′-GAAAACCACA-3′). Further deletion of the 54-bp fragment revealed that a 47-bp fragment containing the five motifs (the 10-bp, 10-bp-like, 10-bp-related, Region 2 and Fifth motifs) is sufficient for suspensor transcription, and represents a cis-regulatory module. A consensus sequence for each type of motif was determined by comparing motif sequences shown to activate suspensor transcription. Phylogenetic analyses suggest that the regulation of G564 is evolutionarily conserved. A homologous cis-regulatory module was found upstream of the G564 ortholog in the Common Bean (Phaseolus vulgaris), indicating that the regulation of G564 is evolutionarily conserved in closely related bean species.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-015-0308-z) contains supplementary material, which is available to authorized users.

Highlights

In most higher plants, the zygote divides asymmetrically to form a small apical cell and a large basal cell with distinct developmental fates (Goldberg et al 1994)
We present experiments identifying two additional cis-regulatory elements within the 54-bp cisregulatory module that are required for G564 suspensor transcription
We show that the Scarlet Runner Bean G564 suspensor cis-regulatory module is conserved in the G564 ortholog (PvG564) of the Common Bean, Phaseolus vulgaris, suggesting that these motifs program G564 expression patterns in the giant suspensors of two closely-related bean species

Summary

Introduction

The zygote divides asymmetrically to form a small apical cell and a large basal cell with distinct developmental fates (Goldberg et al 1994). The apical cell differentiates into the embryo proper, which will become the generation plant; whereas, the basal cell generates the hypophysis and suspensor. The hypophysis will be incorporated into the root meristem of the developing embryo proper (Dolan et al 1993). The suspensor is a terminally differentiated embryonic region that physically connects the embryo proper to the maternal tissues and transports nutrients and growth regulators to the embryo proper before degenerating later during embryogenesis (Yeung and Meinke 1993). The precise mechanisms that determine the developmental fates of the apical and basal cells remain unknown. A number of studies using individual genes and wholegenome transcriptome profiling have shown that different gene sets are activated in the globular-stage embryo proper and suspensor shortly after fertilization

Methods

Discussion

Conclusion