Floral Organogenesis: When Knowing Your ABCs Is Not Enough

Abstract

Flower development is one of the particularly wellestablished model systems for investigating the molecular and genetic mechanisms underlying organogenesis in plants. Over the past 30 years, this work has led to detailed insights into many of the cellular and developmental processes that occur during the formation of flowers. This progress was made possible especially by the identification and characterization of the floral organ identity factors, which specify the different floral organ types in a combinatorial manner. However, in recent years, the genes that act downstream of these master regulators have taken center stage because it has become increasingly clear that they execute many of the functions originally attributed to the floral organ identity factors. In this Update, we will summarize and discuss our current view of floral organogenesis with particular emphasis on recent progress in the field (see "Advances" box). We will briefly describe the latest models for floral organ identity factor function and outline open questions that need to be addressed to better understand how they act at the mechanistic level. Furthermore, we will discuss studies that have begun to reveal how a complex interplay of transcription factors, hormones, regulatory RNAs, and epigenetic modifiers controls different developmental processes during the formation of flowers. Last, we will outline recent efforts to better understand the evolution of flowers and venture a look ahead at likely future developments in the field of flowering research.

Evolution and genetic control of the floral ground plan

“…Many of the regulatory genes identified to date encode transcription factors, and as such their function is to regulate the expression of downstream genes (Thomson et al, 2017). But our knowledge of their direct targets is somewhat ad hoc and requires detailed follow-up of candidates using labour-intensive methods.…”

Was the ancestral angiosperm flower whorled throughout?

“…Unfortunately, to our knowledge, this topic has received comparatively little attention in the literature on genetic regulation of floral development. It is tempting to suggest that the C-class genes that are involved in regulation of stamen and carpel identity as well as flower meristem determinacy (e.g., Mizukami and Ma, 1997;Lenhard et al, 2001;Dreni et al, 2011;Thomson et al, 2017) also influence mechanisms that regulate floral phyllotaxis.…”

Besides and beyond Flowering: Other Roles of EuAP2 Genes in Plant Development

“…They have been linked with aspects of flowering such as flowering time, floral meristem identity and flower morphology [51][52][53]. For recent updates on the ABC floral model see [54][55][56][57] and references therein. However, functional characterization in Arabidopsis and several other plants indicate that euAP2 genes are involved in other developmental processes besides flower development.…”