Conversion of Abaxial to Adaxial Petal in a Torenia (<i>Torenia fournieri</i> Lind. ex Fourn.) Mutant Appeared in Selfed Progeny of the Mutable Line “Flecked”

Abstract

We isolated a torenia mutant "Begonia" from selfed progeny of the mutable line "Flecked," in which the ventral petal of the flower was converted into dorsal petal. In normal-type (NT) flowers, dorsal petals were pale violet and limbs of lateral and ventral petals were violet, whereas the ventral petal had a yellow nectar guide. In contrast, the ventral petal of mutant-type (MT) flowers changed to pale violet, and the nectar guide disappeared. These altered pigmentation patterns were observed from the early stage of corolla pigmentation. Expression analyses of the floral symmetry genes CYCLOIDEA (CYC), RADIALIS (RAD), and DIVARICATA (DIV) showed that TfCYC1, TfCYC2, TfCYC3, and TfRAD1 were mainly expressed in dorsal petals of NT flowers, but in the mutant, these genes were expressed in the ventral petal similar to dorsal ones. These results suggest that conversion of ventral to dorsal petal in the "Begonia" mutant is caused by high expression of TfCYC1, TfCYC2, TfCYC3, and TfRAD1 in the ventral petal, comparable to their expression in dorsal petals.

The CYCLOIDEA–RADIALIS module regulates petal shape and pigmentation, leading to bilateral corolla symmetry in Torenia fournieri (Linderniaceae)

“…A recent study in T. fournieri found broadened expression of CYC ‐ and RAD ‐like genes in dorsalized mutant petals compared with the WT, indicating that these factors may be involved in specifying dorsal corolla identity (Niki et al ., ). Because the violet spots are absent on the dorsal petals, we inferred a negative interaction between the CYC–RAD module and the DV asymmetric pigmentation pattern.…”

Mutation of <i>CYCLOIDEA</i> Expands Variation of Dorsal–ventral Flower Asymmetry Expressed as a Pigmentation Pattern in <i>Torenia fournieri</i> Cultivars

“…The expression levels of genes involved in anthocyanin biosynthesis and floral DV asymmetry were quantified by real-time polymerase chain reaction (RT-PCR) analysis as described previously (Nishijima et al, 2013;Niki et al, 2016). Total RNA was extracted from young corolla at two stages, 3-5 mm and 8-10 mm corolla length.…”

“…A Thermal Cycler DICE Real Time System 800 (Takara Bio) and SYBR Premix Ex Taq (Takara Bio) were used for RT-PCR analysis. The primer sequences and thermal programs used were described previously (Nishijima et al, 2013;Niki et al, 2016). Standard curves were obtained using full-length cDNA in a cloning vector, pGEM T-Easy (Promega Corp., WI, USA).…”

“…The pigmentation pattern of the torenia corolla has also been shown to be controlled by temporal and positional expression of genes involved in regulation of DV asymmetry. We previously isolated a "Begonia" mutant from the "flecked" line which had the active DNA transposon Ttf1 in the genetic background of 'Common Violet' (Niki et al, 2016). Both dorsal and ventral petals are pale in the "Begonia" mutant through dorsalization of the ventral petal.…”

“…Both dorsal and ventral petals are pale in the "Begonia" mutant through dorsalization of the ventral petal. This dorsalization occurred because TfCYC1-3 and TfRAD1, which are orthologs of CYC and RAD, respectively, express both in dorsal and P H A ventral petals (Niki et al, 2016). Su et al (2017) showed that overexpression of TfCYC1, TfCYC2, and TfRAD1 induces dorsalization of petals and represses pigmentation, while knockdown and knockout of these genes by RNAi and CAS9, respectively, induced ventralization of petals, promoting pigmentation.…”