Developmental and genetic basis of the androgynophore in Gynandropsis gynandra.

PREMISE: Flowering plants have evolved a vast array of floral features involved in plant-pollinator interactions. A feature that seemingly increases the chance of pollen transfer is the androgynophore, a stalk-like structure that raises the reproductive organs of the flower. However, little is known about the developmental and genetic basis of this structure despite its presence in multiple, distantly related taxa. Here, we address this gap by investigating Gynandropsis gynandra (Cleomaceae), a species with a prominent androgynophore. METHODS: We combined morphological and anatomical analyses with a comparative transcriptomic study to provide a detailed description of the androgynophore throughout development, examine global gene expression patterns, and identify candidate genes putatively involved in androgynophore elongation. RESULTS: The radially symmetric androgynophore of G. gynandra rapidly lengthens primarily via cell elongation. Despite its structural uniformity, androgynophore development is characterized by complex gene expression patterns including differential expression of floral organ identity genes and genes associated with organ development and growth in Arabidopsis thaliana. CONCLUSIONS: Our morphological characterizations and high-quality transcriptome for G. gynandra suggest that the androgynophore is a novel structure formed via elaboration of both the receptacle and base of reproductive organs because it is structurally like an elongated internode but expresses the genetic repertoire typically associated with the reproductive organs. The drastic increase in cell length and uniform structure elevates the androgynophore as a potentially powerful model for cell elongation.

Exploring the role of auxin in the androgynophore movement in Passiflora.

The flowers of the species belonging to the genus Passiflorashow a range of features that are thought to have arisen as adaptations to different pollinators. Some Passiflora species belonging to the subgenus Decaloba sect. Xerogona, show touch-sensitive motile androgynophores. We tested the role of auxin polar transport in the modulation of the androgynophore movement by applying auxin (IAA) or an inhibitor of auxin polar transport (NPA) in the flowers. We recorded the movement of the androgynophore during mechano-stimulation and analyzed the duration, speed, and the angle formed by the androgynophore before and after the movement, and found that both IAA and NPA increase the amplitude of the movement in P. sanguinolenta. We hypothesize that auxin might have a role in modulating the fitness of these Decaloba species to different pollination syndromes and demonstrate that an interspecific hybrid between insect- and hummingbird-pollinated Xerogona species present a heterosis effect on the speed of the androgynophore movement.

Auxin and physical constraint exerted by the perianth promote androgynophore bending in Passiflora mucronata L. (Passifloraceae).

The androgynophore column, a distinctive floral feature in passion flowers, is strongly crooked or bent in many Passiflora species pollinated by bats. This is a floral feature that facilitates the adaptation to bat pollination. Crooking or bending of plant organs are generally caused by environmental stimulus (e.g. mechanical barriers) and might involve the differential distribution of auxin. Our aim was to study the role of the perianth organs and the effect of auxin in bending of the androgynophore of the bat-pollinated species Passiflora mucronata. Morpho-anatomical characterisation of the androgynophore, including measurements of curvature angles and cell sizes both at the dorsal (convex) and ventral (concave) sides of the androgynophore, was performed on control flowers, flowers from which perianth organs were partially removed and flowers treated either with auxin (2,4-dichlorophenoxyacetic acid; 2,4-D) or with an inhibitor of auxin polar transport (naphthylphthalamic acid; NPA). Asymmetric growth of the androgynophore column, leading to bending, occurs at a late stage of flower development. Removing the physical constraint exerted by perianth organs or treatment with NPA significantly reduced androgynophore bending. Additionally, the androgynophores of plants treated with 2,4-D were more curved when compared to controls. There was a larger cellular expansion at the dorsal side of the androgynophores of plants treated with 2,4-D and in both sides of the androgynophores of plants treated with NPA. This study suggests that the physical constraint exerted by perianth and auxin redistribution promotes androgynophore bending in P. mucronata and might be related to the evolution of chiropterophily in the genus Passiflora.

Rapid touch-stimulated movement in the androgynophore of Passiflora flowers (subgen. Decaloba; Sect. Xerogona): an adaptation to enhance cross-pollination?

Plant touch-sensitive organs have been described since Darwin's observations and are related to a quick response to environment stimuli. Sensitive flower organs have been associated to an increase in the chances of cross pollination but there are few studies regarding this topic. Here we describe for the first time the kinetic of the androgynophore movement of 4 Passiflora species (P. sanguinolenta, P. citrina, P. capsularis, and P. rubra). For that, we collected flowers and recorded the movement after mechano-stimulating the androgynophore. From the recordings, we described the movement regarding its response and sensibility to mechanical stimulus and calculated the duration, speed, and the angle formed by the androgynophore before and after the movement. From our data we were able to propose a link to the pollination habit of these species. The movement of the androgynophore in these Passiflora is a noteworthy floral feature that might lead us to another astonishing example of a mechanism that evolved among angiosperms to assure sexual reproduction.