Expression shifts of floral symmetry genes correlate to flower actinomorphy in East Asia endemic Conandron ramondioides (Gesneriaceae)

Abstract

BackgroundBilateral symmetry flower (zygomorphy) is the ancestral state for Gesneriaceae species. Yet independent reversions to actinomorphy have been parallelly evolved in several lineages. Conandron ramondioides is a natural radially symmetrical species survived in dense shade mountainous habitats where specialist pollinators are scarce. Whether the mutations in floral symmetry genes such as CYC, RAD and DIV genes, or their expression pattern shifts contribute to the reversion to actinomorphy in C. ramondioides thus facilitating shifts to generalist pollinators remain to be investigated. To address this, we isolated putative orthologues of these genes and relate their expressions to developmental stages of flower actinomorphy.ResultsTissue specific RT-PCR found no dorsal identity genes CrCYCs and CrRADs expression in petal and stamen whorls, while the ventral identity gene CrDIV was expressed in all petals. Thus, ventralized actinomorphy is evolved in C. ramondioides. However, CrCYCs still persists their expression in sepal whorl. This is congruent with previous findings that CYC expression in sepals is an ancestral state common to both actinomorphic and zygomorphic core Eudicot species.ConclusionsThe loss of dorsal identity genes CrCYCs and CrRADs expression in petal and stamen whorl without mutating these genes specifies that a novel regulation change, possibly on cis-elements of these genes, has evolved to switch zygomorphy to actinomorphy.Electronic supplementary materialThe online version of this article (10.1186/s40529-018-0242-x) contains supplementary material, which is available to authorized users.

Gene duplication and relaxation from selective constraints of GCYC genes correlated with various floral symmetry patterns in Asiatic Gesneriaceae tribe Trichosporeae

“…One possible explanation for the retaining of multiple GCYC copies is to generate diverse flower morphology that may have resulted from a functional-morphological adaptation for Trichosporeae species to cope with potential pollinator shifts [8, 9, 69, 70]. Positive selection on CYC2 -like copies has been found associated with larger lateral petals (wings) and narrower dorsal petals in Lupinus densiflorus , that play a putative role to attract pollinators for outcrossing [71].…”

“…However, events of reversals from zygomorphy back to actinomorphy are also observed in several angiosperm lineages. Some of these reversions have been regarded as adaptations to rare pollinator and/or low pollination efficiency conditions such as high mountains or deep forests [8, 9].…”

“…myconii (subtribe Ramondinae) and the other four in subtribe Didymocarpinae [10, 13, 14]. The subtribe Didymocarpinae includes the highest number of reversals to actinomorphy, with one event in Conandron [9], one in Tengia (now Petrocodon , see [18]), one in Thamnocharis (now Oreocharis , see [19]) and two in Bournea (now Oreocharis , see [19]) [13, 14, 17, 19]. The multiple reversals to actinomorphy in Trichosporeae make this tribe suitable for studying shifts of floral symmetry correlating to gene expression pattern between closely related zygomorphic and actinomorphic species.…”

Radial or Bilateral? The Molecular Basis of Floral Symmetry

“…The loss of the expression of the CrCYC and CrRAD genes in petals and stamens, and the ubiquitous expression of the CrDIV gene, are associated to the ventralization of the flower. In addition, the co-expression of CrDIV and CrRAD in gynoecium and stamens at the same developmental stage suggest the loss of their antagonistic role in this species [92] (Figure 4B). The tribe Veroniceae is another group of Lamiales where the transition of symmetry from bilateral to radial is observed.…”

Gene Duplication and Differential Expression of Flower Symmetry Genes in Rhododendron (Ericaceae)

“…Additionally, duplications in RAD orthologs have been associated with duplications in CYC orthologs [27]. Similarly, loss of expression or function of CYC orthologs in radially symmetric asterid flowers is correlated with loss of expression or function of RAD orthologs [30,[32][33][34][35][36]. In other cases, ubiquitous expression of RAD orthologs, in conjunction with a CYC ortholog, is correlated with radial symmetry [32,37].…”