Duplications and Expression of DIVARICATA-Like Genes in Dipsacales

Abstract

The genetics underlying flower symmetry shifts between radial and bilateral symmetry has been intensively studied in the model Antirrhinum majus. Understanding the conservation or diversification of this genetic pathway in other plants is of special interest in understanding angiosperm evolution and ecology. Evidence from Antirrhinum indicates that TCP and MYB transcription factors, especially CYCLOIDEA (CYC), DICHOTOMA (DICH), DIVARICATA (DIV), and RADIALIS (RAD) play a role in specifying dorsal identity (CYC, DICH, and RAD) and ventral identity (DIV) in the corolla and androecium of monosymmetric (bilateral) flowers. Previous data indicate that the ECE clade of TCP genes (including CYC and DICH) underwent two duplication events around the diversification of the core eudicots. In this study, we examined the duplication events within Dipsacales, which contains both radially and bilaterally symmetrical flowered species. Additionally, we report here the phylogenetic relationships of the DIV-like genes across core eudicots. Like TCP genes, we found three core eudicot clades of DIV-like genes, with duplications occurring around the diversification of the core eudicots, which we name DIV1, DIV2, and DIV3. The Antirrhinum genes, DIVARICATA and its sister DVL1, fall into the DIV1 clade. We also found additional duplications within these clades in Dipsacales. Specifically, the Caprifoliaceae (bilaterally symmetrical clade) duplicated independently in each of the three core eudicot DIV clades. Using reverse transcription polymerase chain reaction (rtPCR), we showed that most of these copies are expressed across floral tissues in the Dipsacales species Heptacodium miconioides. One copy, DipsDIV1A (orthologous to DIV and DVL1), was expressed in a dorsal-ventral pattern. DipsDIV1A was expressed only in petal tissue, in both dorsal and ventral regions but was lacking from lateral petals. We argue that this suggests that DipsDIV1A may be expressed in a similar pattern to DIV in Antirrhinum, suggesting a broad conservation of this pathway. Finally, DIV contains a large intron near the beginning of the second MYB domain, which shows promise as a highly variable molecular marker for phylogenetic studies.