Temporal-Spatial Transcriptome Analyses Provide Insights into the Development of Petaloid Androecium in Canna indica

Abstract

Canna indica (Zingiberales) is one of the most important ornamental species characterized with beautiful petaloid staminodes, which are considered to evolve from stamens. However, the genetic basis for the development of petaloid staminodes remains unclear largely because the genomic sequences are not available. By using RNA-Seq, we sequenced the transcripts in the flower of C. indica, and quantified the temporal gene expressions in flower primordium and differentiated flower, as well as the spatial gene expressions in petal and petaloid staminode. In total, 118,869 unigenes were assembled, among which 67,299 unigenes were annotated. Quantification analysis identified the differentially expressed genes in the temporal and spatial two comparisons, based on which, Gene Ontology enrichment analysis highlighted the representative terms in each sample, such as specification of organ number in flower primordium, growth in differentiated flower, secondary cell wall biogenesis in petal and cell division in petaloid staminode. Among the 51 analyzed MADS-box unigenes, 37 were up-regulated in differentiated flower compared with those in flower primordium. A-class unigenes were expressed higher in petal than in petaloid staminode, and C-class unigenes were expressed oppositely, whereas B-class unigenes demonstrated close expression levels in these two organs, indicating that petaloid staminode retains stamen identity to some degree. In situ hybridization provided more detailed expression patterns of these unigenes, and revealed the extended expression of B-class to the carpel at later stages when the style turned flat. These results constitute a preliminary basis for the study of flower development in C. indica and can be applied in further study of the evolution of Zingiberales.

Can the anatomy of abnormal flowers elucidate relationships of the androecial members in the ginger (Zingiberaceae)?

“…In Musaceae, for example, a decreased number of stamens in the abnormal flowers of the Dwarf Cavendish banana are the result of the adnation of stamens to the style and the arrested development of some of the stamens which remained dwarf and staminodial [14]. Many of these "abnormal" or "mutant" phenomena have been recognized as homeosis in Cannaceae, they represent a biological phenomenon that caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation), which is important for evolution [39,66]. The abnormal flowers have also been reported in Zingiberaceae, especially in the genus Alpinia; e.g., only two loculi in lateral positions in Hedychium coronarium, two stamens and one sterile appendage in Alpinia vittata [47].…”

Transcriptomic analysis identifies the key genes involved in stamen petaloid in lotus (Nelumbo nucifera)

“…There are four distinct organ types (sepals, petals, stamens, and carpels) that commonly constitute a flower and are arranged in different whorls. For the purpose of ornamentation, petaloid is one of the characteristics selected in ornamental plants breeding [ 5 ]. Based on previous studies on the ranuncukid genus Aquilegia , a model system for studying the evolution of petals [ 6 ], there are two major types of petaloid.…”

Expression and Function Studies of CYC/TB1-Like Genes in the Asymmetric Flower Canna (Cannaceae, Zingiberales)

“…The sequences of CYC/TB1 homologous gene were retrieved from the C. indica inflorescence transcriptome we generated before (Tian et al, 2016) by BLAST similarity searches. Sequence information for the four CiTBL genes is available in GenBank under accession numbers MW176099 to MW176102.…”

“…In vitro transcription was performed using SP6/T7 DIG RNA Labeling Kit (Roche, Basel, Switzerland). Inflorescence and floral tissues were fixed, sectioned, and hybridized to the probes as described previously (Tian et al, 2016(Tian et al, , 2018. The hybridized sections were visualized under brightfield illumination with a Leica DFC550 Microscope (Wetzlar, Germany).…”

“…In the outer whorl, one androecial member develops into a mature petaloid staminode (i.e., infertile stamen) whereas the other two primordia typically abort shortly after initiation (Kirchoff, 1983;Miao et al, 2014). The inner whorl contains two petaloid staminodes plus the fertile stamen, which is in fact a "half-fertile stamen" comprising an anther with a single theca and a petaloid appendage (Kirchoff, 1983;Almeida et al, 2013;Fu et al, 2014;Miao et al, 2014;Tian et al, 2016Tian et al, , 2018. Of the two inner whorl staminodes, one is curved and referred to as the "labellum".…”