The MYB98 subcircuit of the synergid gene regulatory network includes genes directly and indirectly regulated by MYB98

Abstract

SummaryThe female gametophyte contains two synergid cells that play a role in many steps of the angiosperm reproductive process, including pollen tube guidance. At their micropylar poles, the synergid cells have a thickened and elaborated cell wall: the filiform apparatus that is thought to play a role in the secretion of the pollen tube attractant(s). MYB98 regulates an important subcircuit of the synergid gene regulatory network (GRN) that functions to activate the expression of genes required for pollen tube guidance and filiform apparatus formation. The MYB98 subcircuit comprises at least 83 downstream genes, including 48 genes within four gene families (CRP810, CRP3700, CRP3730 and CRP3740) that encode Cys-rich proteins. We show that the 11 CRP3700 genes, which include DD11 and DD18, are regulated by a common cis-element, GTAACNT, and that a multimer of this sequence confers MYB98-dependent synergid expression. The GTAACNT element contains the MYB98-binding site identified in vitro, suggesting that the 11 CRP3700 genes are direct targets of MYB98. We also show that five of the CRP810 genes, which include DD2, lack a functional GTAACNT element, suggesting that they are not directly regulated by MYB98. In addition, we show that the five CRP810 genes are regulated by the cis-element AACGT, and that a multimer of this sequence confers synergid expression. Together, these results suggest that the MYB98 branch of the synergid GRN is multi-tiered and, therefore, contains at least one additional downstream transcription factor.

MYB transcription factor genes as regulators for plant responses: an overview

“…AtMYB16/MIXTA, is proposed to control the shape of petal epidermal cells (Baumann et al 2007), and AtMYB17 is reported to be a putative regulator of early inflorescence development and seed germination ). AtMYB98 regulates synergid cell differentiation during female gametophyte development, pollen tube guidance and the formation of the filiform apparatus (Punwani et al 2008). Similarly, the male germline-specific R2R3 MYB transcription factor DUO1 POLLEN1 (DUO1) is reported to have an essential role in sperm cell differentiation in Arabidopsis (Borg et al 2011).…”

The R2R3 MYB Transcription Factor DUO1 Activates a Male Germline-Specific Regulon Essential for Sperm Cell Differentiation inArabidopsis

“…In the male gametophyte, a pioneering study established a late pollen regulatory network governed by five pollen-specific MIKC* MADS box proteins that is important in the vegetative cell for pollen maturation (Verelst et al, 2007a(Verelst et al, , 2007b. A corresponding example in the female gametophyte is a regulatory network modulated by the R2R3-type MYB transcription factor MYB98, which regulates a battery of synergid cell-expressed genes that are required for pollen tube guidance and formation of the filliform apparatus (Punwani et al, 2007). In terms of the gametes, transcriptional regulation is likely to be an important aspect in germline development as plant male germ cells have a distinct and diverse transcriptome (Engel et al, 2003;Okada et al, 2006;Borges et al, 2008).…”

Achievement of genetics in plant reproduction research: the past decade for the coming decade

“…It is expressed in synergid cell and the egg cell, and it can attract the pollen tube at the micropyle of the ovule. In Arabidopsis, synergid cell-factors, MYB98 (Kasahara et al, 2005;Punwani et al, 2007) and FERONIA/SIRENE (Escobar-Restrepo et al, 2007), have also been identified for their micropylar pollen tube guidance and pollen tube reception. In all cases, the synergid cell is likely to be a key player for successful guidance of the pollen tube into the female gametophyte for successful fertilization.…”