MADS-domain transcription factors and the floral quartet model of flower development: linking plant development and evolution

Abstract

The floral quartet model of floral organ specification poses that different tetramers of MIKC-type MADS-domain transcription factors control gene expression and hence the identity of floral organs during development. Here, we provide a brief history of the floral quartet model and review several lines of recent evidence that support the model. We also describe how the model has been used in contemporary developmental and evolutionary biology to shed light on enigmatic topics such as the origin of land and flowering plants. Finally, we suggest a novel hypothesis describing how floral quartetlike complexes may interact with chromatin during target gene activation and repression.

Sex is determined by XY chromosomes across the radiation of dioeciousNepenthespitcher plants

“…Two SEP1 ‐linked SNPs were heterozygous in 27 of 28 males, whereas 21 of 22 females were homozygous, consistent with the existence of strongly X‐ and Y‐linked copies. If SEP homologs in Nepenthes are involved in the determination of floral organ identity (as in A. thaliana , Theißen et al ), the sex‐linked Nepenthes SEP1 homolog could be involved in unisexual flower development. In particular, sequence differences between the Nepenthes SEP1 X‐ and Y‐linked copies might modify their functions such that they suppress the development of either carpels or stamens.…”

Recent advances in understanding the roles of whole genome duplications in evolution

“…Some of these were characterised more than 20 years ago for their ability to interact with each other in different combinations to specify the floral organs of Antirrhinum (snapdragon) and Arabidopsis . In these seminal studies, homeotic floral mutants were used to deduce an elegant ‘ABC model’, later elaborated into an ‘ABCDE model’ that explains how the four concentric whorls of sepals, petals, male stamens and female carpels develop in these flowers 17– 19 . A-function genes specify sepals; A, B and E are needed to make petals; B, C and E male stamens; C female carpels; and D for ovules.…”

“…In homeotic mutants lacking B-function, for example, sepals replace petals and carpels replace stamens 18 . Most of the A, B, C, D and E functions are performed by combinations of MADS-box transcription factors that operate as homodimers and heterodimers and tetramers with different selectivities for binding to variants of a common motif in the promoters of target genes 19, 20 . Hence, they target overlapping but distinct sets of floral identity genes many of which are themselves ohnologues 21 .…”

“…An A/E gymnosperm pro-orthologue gave rise to angiosperm A and E genes, and further duplicated A genes were also retained after the ε WGD 19, 21– 24 . These duplicated and diversified gene sets organised to generate the first now-extinct flowers, and recent reconstructions suggest that these were bisexual with petal-like tepals and pollen-bearing stamens arranged in multiple concentric whorls, and female carpels in a central spiral 25 .…”

Synteny-based phylogenomic networks for comparative genomics

“…One application is to extract and visualize syntenic relationships for certain genes or gene families across and within species (depending on the question at hand). For example, APETALA3 (AP3) and PISTILLATA (PI) genes are important MADS-box transcription factors that specify petal and stamen identity (known as B-class floral regulatory genes) (Dodsworth, 2016;Theissen et al, 2016). A previous comparative study of floral MADS-box genes between the sister families Cleomaceae (Tarenaya hassleriana) and Brassicaceae (e.g.…”