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. 2018 Oct 29;59(1):24.
doi: 10.1186/s40529-018-0242-x.

Expression Shifts of Floral Symmetry Genes Correlate to Flower Actinomorphy in East Asia Endemic Conandron Ramondioides (Gesneriaceae)

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Free PMC article

Expression Shifts of Floral Symmetry Genes Correlate to Flower Actinomorphy in East Asia Endemic Conandron Ramondioides (Gesneriaceae)

Kuan-Ting Hsin et al. Bot Stud. .
Free PMC article

Abstract

Background: Bilateral 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.

Results: Tissue 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.

Conclusions: The 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.

Keywords: Bilateral symmetry; CYCLOIDEA; DIVARICATA; Peloria; RADIALIS; Reversal; Zygomorphy.

Conflict of interest statement

The authors declare that they have no competing interests. And there have neither financial competing interests nor other competing interests.

Figures

Fig. 1
Fig. 1
The flower of C. ramondioides from early to late stage. Early, middle and late stage corresponding to Stage 10, 13, 15 in Additional file 1: Table S1. Actinomorphy was observed in late stage C. ramondioides flower. Scale bar represented 1 cm
Fig. 2
Fig. 2
The SEM photos of morphological development process of Conandron ramondioides flowers. Zygomorphy was observed at Stage 3 of sepal whorl. Definition of developmental stages of C. ramondioides based on (Harrison et al. 1999). a Stage 3, the sepals form as bulges at the points of the pentagon. b Stage 4, the sepals grow, while the floral meristem remains undifferentiated. c Stage 6, the corolla and androecium grow, and the gynoecium initiates. d Stage 7A, petal growth. e Stage 7B, androecium and gynoecium development. f Floral diagram of C. ramondioides. Se Sepals, Pe petals, S stamen, G gynoecium. Scale bar represents 50 μm
Fig. 3
Fig. 3
Alignments of protein sequences of CrCYC, CrRAD and CrDIV genes with homologs from Antirrhinum majus (CYC, RAD and DIV) and Bournea leiophylla (BlCYC1, BlCYC2, BlRAD, BlDIV1 and BlDIV2). a Alignmentes of CYC homologs. TCP, ECE and R domain are outlined. Identical amino acids are in black and similar amino acids are in gray. b Alignments of RAD homologs. MYB domain are outlined. c Alignments of DIV homologs. Two MYB domains (R2 and R3) are outlined. A highly conserved SHAQKY motif in R3 MYB domain is identified and labelled in white box. Arrows indicate sequence region used in phylogeny analysis. Sequence region used in phylogenetic analysis coving almost all important domains in all three gene dataset except for PlDIV in DIV dataset
Fig. 4
Fig. 4
Neighbour-joining trees of CYC-like, RAD-like and DIV-like genes. Trees from a to c are reconstructed based on amino acid sequences. a CYC is from A. majus, others are CYC-like genes from Gesneriaceae species (see Additional file 2: Table S2). Trees show CrCYCs cluster into three groups with high support. b The tree shows CrRADs cluster into two distinct clade with high support. c Bootstrap values from NJ and ML are listed above and below branches respectively. Bootstrap values > 70 are shown. Detailed sequences information is listed in Additional file 2: Table S2
Fig. 5
Fig. 5
Gene-specific reverse transcriptase polymerase chain reaction (RT-PCR) analysis of CrCYC, CrRAD and CrDIV genes from C. ramondioides buds and dissected flower tissues. E, M, L represent three flower development stage defined in this study. E stands for early flower development stage; M stands for middle flower development stage; L stands for anthesis stage. P1 to P5 represent dissected petal from flower bud at early (E) flower developmental stage. Sep, Pe, Sta and gyn denote pooled sepals, pooled petals, pooled stamens and gynoecium dissected from early flower developmental stage. CrCYC1C, CrCYC1D and CrCYC2 indicate expression of CrCYC1C, CrCYC1D and CrCYC2. CrRAD1 and CrRAD2 indicate expression of CrRAD1 and CrRAD2. CrDIV indicates expression of CrDIV. 18S is included as a positive control. CrCYC1C, CrCYC1D, CrRAD1, CrRAD2 and CrDIV are detected through flower development stages, only CrCYC2 is restricted through flower development stages. CrDIV is detected in all petals, whereas CrCYC1C, CrCYC1D, CrCYC2, CrRAD1 and CrRAD2 are restricted in petals. CrCYC1C and CrCYC2 were detected in pooled sepal tissue

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