Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Zhang, Jingbo [1], Bukhari, Ghadeer [2], Zhang, Wenheng [3].

Floral symmetry genes and the evolution of floral zygomorphy in Solanaceae.

Comparative studies demonstrated that independent origins of floral zygomorphy are associated with redeployment of CYCLOIDEA2 (CYC2)-like genes at least six times in core eudicots. It is, however, unclear whether parallel genetic mechanisms exist since there were an estimated 125 independent origins of floral zygomorphy in angiosperms. Recent work indicated that the most recent common ancestor of Solanaceae possessed zygomorphic flowers. Most interestingly, the developmental process of floral zygomorphy is unique and associated with its sophisticated sympodial inflorescence in Solanaceae. We have used a candidate gene approach to study the evolution and expression of CYC2s in solanaceous species, with the intent to characterize the genetic basis of floral zygomorphy development in this family. We identified two major sequence types of CYC2 in Solanaceae, CYC2A and CYC2B, which result from a gene duplication that occurred before the diversification of the family. In zygomorphic-flowered species of Solanaceae, the CYC2A genes are expressed in androecium and gynoecium but the spatial patterns are divergent among species, while the CYC2B genes are expressed consistently in the dorsal region of the zygomorphic calyxes. In Schizanthus pinnatus and Schizanthus grahamii, two CYC2A paralogs resulting from a Schizanthus-specific gene duplication are expressed with reciprocate patterns in androecia that match their zygomorphic morphology. That is, CYC2A-1 is expressed mainly in the two aborted dorsal and one aborted ventral stamen, while CYC2A-2 is expressed in the two functional lateral stamens. The differential expression of CYC2A along the dorsoventral plane of androecia was also detected in other three zygomorphic-flowered species, Calibrachoa elegans, Nicotiana obtusifolia, and Browallia speciose, but the expression patterns do not closely match their zygomorphic morphology. Furthermore, RNA in situ hybridization indicated that the CYC2A-2 detected in functional stamens in Sc. pinnatus is expressed across the floral meristem at early stages and exclusively within the pollen sacs and ovules at the late stages of floral development. Surprisingly, none of the CYC2 genes were found differentially expressed in the zygomorphic corollas of species of Solanaceae, which is confirmed by RNA-seq results in Sc. grahamii and Sc. pinnatus with strong zygomorphic corollas. Overall, our results suggest that the molecular basis underlying floral symmetry evolution is complicated in Solanaceae and the genetic mechanisms underlying the development of their zygomorphic corolla are likely to be independent from the CYC2 program, which may reflect the responses to different evolutionary and developmental contexts in this core eudicot clade.

1 - Department Of Biology, Virginia Commonwealth University, 1000 West Cary Street, Life Science Building 336, Richmond, VA, 23284, United States
2 - Virginia Commonwealth University, 1000 W Cary Street, Richmond, VA, 23284.0, United States
3 - Virginia Commonwealth University, Department Of Biology, 1000 W Cary Street, Richmond, VA, 23284, United States

Keywords:
CYC2-like genes
Floral evolution
floral symmetry
gene duplication
gene expression
RNA-Seq
Schizanthus
Solanaceae.

Presentation Type: Oral Paper
Session: 20, Evolutionary Developmental Biology (Evo-Devo) I
Location: 113/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 10:15 AM
Number: 20009
Abstract ID:932
Candidate for Awards:None