Gynoecium Patterning in Arabidopsis: A Basic Plan Behind a Complex Structure

Abstract

The Arabidopsis gynoecium consists of two congenitally fused carpels that, at maturity, form a bilocular chamber protecting the ovules and placentae produced by the meristematic regions of the carpel margins. This meristematic region also gives rise to a style capped with stigmatic papillae at the apical end of the developing gynoecia and a transmitting tract that connects the stigma to the ovule‐bearing chambers. Most data point towards a common evolutionary origin of leaves and carpels and suggest that leaves can be transformed to carpels by expressing only a few carpel identity genes. In this review, we have therefore approached the carpels from the leaf‐like organ hidden within by stressing the parallels between leaf and carpel development. Many of the genes with a role in leaf development were first identified by the effect their mutations cause in carpel development, suggesting that the regulatory networks may be more robust in leaves than in the more complex and evolutionary younger carpels. Similar genetic networks ensure the maintenance of adaxial–abaxial, proximal–distal and medial–lateral dichotomies in leaves and carpels. Data have emerged showing that crosstalk and redundancies are characteristics of these pathways, as well as a general interplay of hormonal balances, with auxin as a major morphogen.

Unique and overlapping functions for the transcriptional regulators KANADI1 and ULTRAPETALA1 in Arabidopsis gynoecium and stamen gene regulation

“…The adaxial–abaxial axis forms early during gynoecium development and distinguishes the outer (abaxial) valve and replum tissues from the inner (adaxial) ovules, placenta, septum, and transmitting tract (Larsson et al, 2013). The apical–basal axis becomes specified shortly thereafter as the organ grows vertically into a tube‐shaped organ (Sundberg & Ferrandiz, 2009). Along this axis, the apical stigmatic tissue sits atop the gynoecium as the site of pollen deposition, the underlying style supports growth of the pollen tubes into the central ovary, and the basal gynophore connects the gynoecium to the rest of the flower.…”

“…The stamens consist of an anther and subtending filament and contain the pollen, the male gametophytes, whereas the central gynoecium is composed of one or more fused or unfused carpels and contains the embryo sacs, the female gametophytes. After fertilization, the gynoecium matures into a fruit that nourishes the developing embryos until seed dispersal (Sundberg & Ferrandiz, 2009). The mature fruits of many plants are harvested and their fleshy parts and/or seeds are consumed by animals.…”