EOBII Controls Flower Opening by Functioning as a General Transcriptomic Switch    

Abstract

R2R3-MYB transcription factors (TFs) are involved in diverse aspects of plant biology. Recently an R2R3-MYB was identified in Petunia x hybrida line P720 to have a role in the transcriptional regulation of floral volatile production. We propose a more foundational role for the R2R3-MYB TF EMISSION OF BENZENOIDS II (EOBII). The homolog of EOBII was isolated and characterized from P. x hybrida 'Mitchell Diploid' (MD) and Nicotiana attenuata. For both MD and N. attenuata, EOBII transcript accumulates to high levels in floral tissue with maximum accumulation at flower opening. When EOBII transcript levels are severely reduced using a stable RNAi (ir) approach in MD and N. attenuata, ir-EOBII flowers fail to enter anthesis and prematurely senesce. Transcript accumulation analysis demonstrated core phenylpropanoid pathway transcripts and cell wall modifier transcript levels are altered in ir-EOBII flowers. These flowers can be partially complemented by feeding with a sucrose, t-cinnamic acid, and gibberellic acid solution; presumably restoring cellular aspects sufficient for flower opening. Additionally, if ethylene sensitivity is blocked in either MD or N. attenuata, ir-EOBII flowers enter anthesis. These experiments demonstrate one R2R3-MYB TF can control a highly dynamic process fundamental to sexual reproduction in angiosperms: the opening of flowers.

Jasmonoyl-l-Isoleucine Coordinates Metabolic Networks Required for Anthesis and Floral Attractant Emission in Wild Tobacco (Nicotiana attenuata)

“…Silencing the expression of the MYB305 homolog EOBII in petunia (Petunia hybrida) results in floral corollas that fail to enter anthesis, whereas in MYB305-silenced N. attenuata plants, flowers abscised prematurely (Colquhoun et al, 2011). However, while the accumulation of MYB305 transcripts was also delayed in dissected corolla tissues of ir-coi1 and ir-aoc flowers, maximal levels at the onset of anthesis were similar to those of wildtype corollas at anthesis ( Figure 3B).…”

“…[See online article for color version of this figure. ] quantified corolla transcript levels of central JA biosynthesis genes from 1 DAP until anthesis ( Figures 3A and 3B). We additionally measured the transcript levels of JAZd, a recently identified transcriptional repressor of JA accumulation in complete N. attenuata flowers (Oh et al, 2013), and Na-MYB305, the N. attenuata homolog of Arabidopsis MYB21, a transcription factor in various plant species known for its role in floral development (Liu et al, 2009;Colquhoun et al, 2011;Reeves et al, 2012). Expression of the N. attenuata JA biosynthesis transcripts AOS (Kallenbach et al, 2012) and THREONINE DEAMINASE (TD) (Kang et al, 2006) peaked in wild-type, ir-aoc, and ir-coi1 corollas at 1 DAP and decreased in conjunction with corolla expansion ( Figure 3B).…”

The R2R3-MYB–Like Regulatory Factor EOBI, Acting Downstream of EOBII, Regulates Scent Production by Activating ODO1 and Structural Scent-Related Genes in Petunia

“…EMISSION OF BENZENOIDS II (EOBII), similar to PAP1 and in contrast with ODO1, has been shown to regulate the transcription of both shikimate pathway genes and genes directly involved in the biosynthesis of phenylpropanoid volatiles (Verdonk et al, 2005;Dare et al, 2008;Ben Zvi et al, 2008;Spitzer-Rimon et al, 2010;Zvi et al, 2012). While it has been recently suggested that EOBII may also have activities outside the scope of floral scent production (Colquhoun et al, 2011b), the epistatic relations between EOBII and ODO1 have been confirmed: EOBII binds directly to ODO1's upstream regulatory sequence and transcriptionally activates its expression (Van Moerkercke et al, 2011).…”

Biosynthesis of floral scent 2-phenylethanol in rose flowers

“…19) The EOBII homolog isolated from Petunia x hybrida "Mitchell Diploid" and Nicotiana attenuate is involved in the sexual reproduction process of flower opening. 20) There has been a rapid progress in elucidating the biosynthetic pathways, enzymes, and genes involved in the formation of plant volatile compounds, which has enabled the investigation of their physiology and function at the molecular and biochemical basis. 21) Roses are called the "queen of scents" because of the attractive and sweet odor that they emit.…”