RNA-Seq analysis reveals the distinctive adaxial–abaxial polarity in the asymmetric one-theca stamen of Canna indica

Abstract

Proper establishment of adaxial-abaxial polarity is essential for the development of lateral organs, while former researches were mostly focused on the polarity regulation in leaves, and little is known in stamens, especially in the asymmetric ones. Canna indica (Zingiberales: Cannaceae) is a widely cultivated ornamental plant and the representative species to study the evolutionary development of Zingiberales. The androecium of Canna indica comprises 3-4 petaloid staminodes and a fertile stamen (FS), which consists of a one-theca anther and a petaloid appendage. The partially petaloid stamen is considered as an intermediate state organ from a two-thecae stamen to a completely petaloid staminode. Using RNA-Seq, we quantified the expressions of the transcripts in anther and petaloid appendage, and detected 64,430 and 57,041 unigenes in these two organs, respectively. 4574 unigenes were down-regulated, and 3525 were up-regulated in petaloid appendage compared with those in anther. GO enrichment analysis indicated that the function of cytokinin is more related to cell differentiation in anther, while auxin is more to cell division in petaloid appendage. B- and C-class floral homeotic genes were expressed in these two androecium parts. Most of the class III HD-ZIP family members, which specify adaxial identity, were expressed lower in petaloid appendage than in anther; while KANADIs and YABBYs, which promote abaxial identity, exhibited opposite expression patterns. In situ hybridization showed that the adaxial marker gene was mainly expressed in the region between the two protrusions of the anther, while the abaxial marker was mainly expressed in petaloid appendage. We hypothesize that the adaxial-abaxial polarity participates in the distinctive anther-petaloid appendage patterning within the asymmetric FS of Canna indica.

Irregular adaxial–abaxial polarity rearrangement contributes to the monosymmetric-to-asymmetric transformation of Canna indica stamen

“…We used CiPHB1 and CiFIL as the marker genes for adaxial and abaxial polarities respectively ( Tian et al 2018 ), and examined their expression patterns in developing flowers using in situ hybridization.…”

“…Later, CiPHB1 transcripts were detected in different organs including petals, petaloid staminodes, stamen, carpels, and pedicels ( Fig. 3B–E ; Tian et al 2018 ). Expression was also observed in the developing vascular bundles ( Fig.…”

“…As the signal of CiPHB1 faded in the connective region ( Fig. 4D ), CiFIL transcripts lost their abaxial preference, and started to accumulate in the petaloid appendage primordium slightly ( Tian et al 2018 ). Eventually, CiFIL expression contracted to the margin of the petaloid appendage ( Fig.…”

“…Flowers of C. indica (Cannaceae) comprise 3–4 (occasionally five) petaloid staminodes and a half-petaloid stamen. The stamen consists of a one-theca anther and an associated petaloid appendage and exhibits an asymmetric pattern ( Kirchoff 1983 ; Rudall and Bateman 2004 ; Miao et al 2014 ; Tian et al 2018 ).…”

“…In our previous research, ectopic expression of PHB was shown to inhibit the development of microsporangium in the stamen of arabidopsis, whereas PHB normally promotes the formation of the internal boundary between inner and outer microsporangia within the anthers ( Li et al 2019 ). We have undertaken a preliminary analysis of the adaxial–abaxial polarity in the asymmetric stamen of C. indica ( Tian et al 2018 ), but the detailed structural patterning process of the asymmetric stamen which, significantly, controls the symmetry of the whole flower, is not well understood. In this study, we examined the adaxial–abaxial polarity throughout the stamen development process of C. indica , and used the monosymmetric stamens of Alpinia galanga (Zingiberaceae) and arabidopsis as necessary contrasts.…”